EP1885553A2

EP1885553A2 - Ballistic laminate structure

Info

Publication number: EP1885553A2
Application number: EP06760019A
Authority: EP
Inventors: Lawrence J. Dickson
Original assignee: Composix Co
Current assignee: Composix Co
Priority date: 2005-05-18
Filing date: 2006-05-17
Publication date: 2008-02-13
Also published as: WO2006124995A2; WO2006124995A3; WO2006124995B1

Abstract

A ballistic structure having at least one laminate sheet of a plurality of fiber bundles is disclosed. The laminate sheet has adhesive resin on at least one surface thereof, without substantial penetration of the adhesive resin into the fiber bundles. In embodiments having more than one laminate sheet, the inter-laminate shear strength between the laminate sheets is controlled to control ballistic effectiveness of the ballistic structure.

Description

BALLISTIC LAMINATE STRUCTURE

[0001] The present invention relates to a ballistic structure, and, more particularly, to a laminate sheet having a plurality of fiber bundles and other ballistic structures incorporating such a laminate sheet.

BACKGROUND

[0002] Fiber bundles arranged as a laminate sheet are often used with ballistic structures. Generally, fiber bundles are arrayed and laminated to form the laminate sheet. A laminate sheet may also include several arrays arranged as layers in the laminate sheet. The laminate sheet may be used in soft body armor, as backing for a ceramic or other facing in hard armor, or in other ballistic applications.

[0003] Typically, the fiber bundles in an array are adhered with a polymeric resin or other adhesive. The resin or adhesive penetrates the bundles and forms a matrix around individual fibers in the bundles as well as adhering adjoining bundles. Two or more layers of these arrays are then laminated together.

[0004] Some conventional laminate sheets are formed without the use of a resin or adhesive matrix encapsulating the fibers. These sheets are formed with no adhesive or resin adhering the fibers or the fiber bundles together, but with a thin polymeric film that is placed on the surface of the fiber bundles in the layers or arrays to be laminated and subjected to high temperature and/or pressure. The high temperature/pressure forces the polymeric film into surface interstices in the arrays and, when cooled, adheres the adjacent arrays as a laminate sheet. There is no separate adhesive or resin applied to the fiber bundles to adhere the arrays, and the polymeric film does not penetrate into the fiber bundles. SUMMARY OF THE INVENTION

[0005] One embodiment of the present invention includes a laminate sheet with at least one layer of unidirectionally-oriented fiber bundles bound together with a discontinuous array of adhesive or resin. This resin or adhesive does not substantially penetrate the fiber bundle to encapsulate or form a matrix around a substantial number of individual fibers in the bundle. The resin makes up no more than about 20% by weight of the total laminate.

[0006] One embodiment of the present invention provides a laminate sheet having at least two layers of unidirectionally-oriented fiber bundles with a release layer provided between the fiber bundle layers. The fiber bundle layers are also provided with an adhesive on their surface, between the fiber bundle and the release layer. The adhesive adheres the fiber bundles as a sheet and provides some bonding to the release layer.

[0007] Neither the adhesive nor the release layer substantially penetrates the fiber bundle and no resin or adhesive matrix is formed encapsulating a substantial number of fibers. The film layer does not act as the sole adhesion layer for the fiber bundle layers. This release layer exhibits poor bonding qualities to the adhesives on the surface of the fiber bundle layers and helps minimize inter-laminar shear during ballistic impact.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the accompanying drawings, which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to exemplify the embodiments of this invention.

[0009] Figure 1 is a representational view of a layer of fiber bundles with adhesive on one side;

[0010] Figure 2 is a representational view of a layer of fiber bundles adhesive on both sides;

[0011] Figure 3 is a representational view of two layers of fiber bundles;

[0012] Figure 4 is a representational view of a layer of fiber bundles and a release layer; [0013] Figure 5 is a representational view of two layers of fiber bundles and release layers;

[0014] Figure 6 is a representational view of two layers of fiber bundles and release layers; and

[0015] Figure 7 is a representational view of another embodiment of two layers of fiber bundles and release layers.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention relates to a ballistic material suitable for use in armor applications, particularly lightweight armor applications. The material is suitable for use in, among other uses, hard armor panels, for use behind ceramic or other materials as a backing, and as a soft armor material for body armor.

[0017] A basic laminate of unidirectionally-oriented fiber bundles is formed in which an adhesive is applied to the surface of the fiber bundles. The adhesive may be in the form of a discontinuous array of resin. The adhesive adheres the fiber bundles into an array or layer. The adhesive does not substantially penetrate into the fiber bundles and no resin or adhesive matrix is formed encapsulating a substantial number of fibers.

[0018] The adhesive forms a discontinuous array and is no more than about 20% by weight of the total laminate. Preferably, the adhesive is less than about 12% by weight of the total laminate, for example, less than 10% by weight, and, more preferably, less than about 5% by weight of the total laminate. The discontinuous array of adhesive may be applied in any manner, such as application in powder form with subsequent fusing to the fiber array, randomly dispersed continuous or chopped filaments head fused to the fiber array, or application of a non-woven array of thermoplastic adhesive, such as a hot-melt adhesive web, for example, that sold under the trademark Spunfab^®, sold by Spunfab Corporation, Cuyahoga Falls, Ohio. Another example of a suitable adhesive is powdered resin, such as sold under the trademark Saran 506 by Dow Chemical Company.

[0019] More than one layer of this basic laminate may be combined to provide more complex laminates having at least two layers, and preferably fewer than ten layers, of the basic laminate. Such combination may be effected, for example, by a combination of heat and pressure applied to two or more basic laminates. The complex laminate is preferably a combination of basic laminates stacked and laminated in such a way as to retain flexibility. These complex laminates may also then be stacked, layered, or combined to provide, for example, a thick, rigid armor product.

[0020] Control of the inter-laminar shear properties between the layers of the basic laminate, or between layers of the more complex laminates, can improve the effectiveness of the material as a ballistic material.

[0021] In one embodiment, a release layer is provided between adjacent layers of fiber bundles, or basic laminates, to control inter-laminar shear. The release layer is a poor adhesion layer applied to the adhesive layer, but does provide some bonding to the adhesive layers. The release layer provides a low inter-laminar shear strength between the fiber bundle layers to facilitate inter-laminar debonding at the point of impact of a ballistic event. The release layer reduces bonding strength between the layers by at least about 15% compared to a laminate without a release layer, as defined by a climbing drum peel test in accordance with ASTM D1781-98 (2004).

[0022] The release layer applied to the structure may be in the form of:

1. a spun adhesive web, film, or powder that is applied and does wet out the fiber during processing;

2. a wet resin release layer that does not wet out the fiber;

3. a wet release layer that does wet out the fiber;

4. a continuous film layer that does not wet out the fiber; or

5. a combination of the above.

[0023] Use of the term "wet out" indicates substantial penetration of the material into the fiber bundle.

[0024] A suitable release layer is polyethylene terephthalate film, such as made by Mitsubishi Polyester Film Group, having a minimum thickness of about 0.00005 inch thick. Polyethylene film is also suitable for the release layer, such as polyethylene film with a thickness of about 0.0035 inch. Polyethylene film having thickness of about 0.002 inch (2 mil), 0.001 inch (1 mil) , or 0.0005 inch (0.5 mil) or less is also suitable. Other materials are also suitable and may be selected without undue experimentation and without departing from the spirit and scope of the invention. Selection of different combinations of materials for the release layer and the adhesives may result in different inter-laminar shear characteristics to accommodate different ballistic needs.

[0025] The release layer is a layer of continuous or perforated material that is the connecting link between the layers. In one embodiment, the adhesive layer sticks to the fibers and filaments, and also sticks to the release layer. Li this embodiment, the release layer need not stick to the fibers or filaments to make a laminate structure, it just needs to stick to the adhesive layer, which is stuck to the fibers. This is particularly suitable when the laminates are molded at low pressures (e.g., vacuum bag process (14psi)), where there is not enough pressure to force the film past the adhesive layer and into the fiber or where the release layer melts at a higher temperature than the adhesive layer. As discussed in greater detail below, this release layer reduces the inter-laminar shear strength between layers compared to the shear strength between the layers if the release layer is not present. If it weren't present, the adhesive layers would stick to each other and provide a higher inter-laminar shear and a lower ballistic result.

[0026] The laminate may be structured with release layers to reduce inter-laminar shear strength between individual basic laminate layers, between complex laminate layers, or a combination thereof.

[0027] Figure 1 illustrates a first fiber bundle layer 10 with a plurality of fiber bundles 12 arranged unidirectionally. An adhesive layer 14 is applied to a top surface 16 of the fiber bundle layer 10.

[0028] Figure 2 illustrates a single fiber bundle layer 10 having an adhesive layer 14 applied to both the top surface 16 and a bottom surface 18 thereof. The adhesive in the adhesive layer 14 may be a first adhesive or a second adhesive.

[0029] Figure 3 illustrates a structure with the first fiber bundle layer 10 and a second fiber bundle layer 20 arranged perpendicularly to the first fiber bundle layer 10. In this embodiment, the adhesive present on the top surface 16 of the first fiber bundle layer 10 is a different adhesive than is present on the bottom surface 18 of the second fiber bundle layer 20. The first adhesive and the second adhesive both bond to the fiber substrates, and may have poor bonding properties relative to the other adhesive, such that localized de-bonding between the first layer and the second layer occurs at the point of ballistic impact. This serves to reduce the inter-laminar shear strength between the layers.

[0030] Figure 4 illustrates the first fiber bundle layer 10 with adhesive layers 14 on both the top surface 16 and the bottom surface 18. A release layer 22 is applied to the adhesive layer 14 on the top surface 16. The release layer 22 has poor adhesion to the adhesive layer 14, but does have limited adhesion to the adhesive layer 14.

[0031] Figure 5 illustrates a structure with first fiber bundle layer 10 and second fiber bundle layer 20. Both fiber bundle layers 10, 20 have an adhesive layer 14 applied to the top surface 16 and the bottom surface 18. A release layer 22 is applied to the adhesive layer 14 on the top surface 16 of the first fiber bundle layer 10. The release layer 22 is between the first fiber bundle layer 10 and the second fiber bundle layer 20. Optionally, a release layer 22 is applied to the adhesive layer 14 on the top surface of the second fiber bundle layer 20.

[0032] Figure 6 illustrates a structure with first fiber bundle layer 10 and second fiber bundle layer 20. Both fiber bundle layers 10, 20 have an adhesive layer 14 applied to the top surface 16 and the bottom surface 18. A release layer 22 is applied to the adhesive layer 14 on the bottom surface 18 of the first fiber bundle layer 10 and a release layer applied to the top surface 16 of the second fiber bundle layer 20. The adhesive on the top surface 16 of the first fiber bundle layer 10 and the bottom surface 18 of the second fiber bundle layer 20 are different adhesives that both bond to the fiber substrates, but have poor bonding properties relative to the other adhesive.

[0033] Figure 7 illustrates a structure with first fiber bundle layer 10 and second fiber bundle layer 20. Both fiber bundle layers 10, 20 have an adhesive layer 14 applied to the top surface 16 and the bottom surface 18. A release layer 22 is applied to the adhesive layer 14 on the top surface 16 of the second fiber bundle layer 20. As above, the adhesive on the top surface 16 of the first fiber bundle layer 10 and the bottom surface 18 of the second fiber bundle layer 20 may be different adhesives that both bond to the fiber substrates, and may have poor bonding properties relative to the other adhesive. [0034] While the Figures illustrate structures having only two fiber bundle layers, it is within the spirit and scope of the invention for more than two fiber bundle layers to be provided in a single structure. As otherwise described herein, a complex laminate has a plurality of basic laminates, preferably fewer than ten basic laminates. Such a complex laminate may be used individually or stacked or layered with other complex or basic laminates to accommodate the particular ballistic need. The inter-laminar shear strength between basic laminates within a complex laminate and/or between complex laminates may be controlled to accommodate the particular ballistic need. This control of the inter-laminar shear strength between complex laminates may be accomplished by use of selected adhesives and/or selected release layers, as described herein relative to control of inter-laminar shear strength between fiber bundle layers.

[0035] As illustrated in the Figures, the placement of the release layer and the adhesive layer may be varied depending on the particular ballistic application encountered. For example, another layer added on top of second fiber bundle layer 20 in Figure 7 could be provided with any suitable adhesive on its bottom surface 18, and the release layer 22 on the top surface 16 of the second fiber bundle layer would be disposed between the added fiber bundle layer and the second fiber bundle layer 20.

[0036] Another fiber bundle layer added below the first fiber bundle layer 10 in Figure 7 could have either an adhesive layer 14 on its top surface 16 with an adhesive different from the adhesive in the adhesive layer 14 on the bottom surface 18 of the first fiber bundle 10 or a release layer 22 disposed on the adhesive layer 14 on its top surface 16. The arrangements and configurations of the adhesives and the release layers in adjacent fiber bundle layers are chosen to have poor adhesion with the surface of the immediately adjacent fiber bundle layer.

[0037] Complex laminates having more than one basic laminate, and preferably fewer than ten basic laminates, may be formed with selective release layers and selected adhesives between predetermined layers to accomplish the desired ballistic effectiveness. For example, in a complex laminate of four basic laminates, there may be a release layer between the first and second basic laminate and between the third and fourth basic laminate, with no release layer between the second and third basic laminate. Or there may be selected adhesives between the first and second basic laminate and no other release layer or adhesive chosen for poor adhesiveness with an adjacent layer in the remaining part of the complex laminate. [0038] Also, complex laminates having at least two basic laminates may be combined in which the inter-laminar layer between the complex laminates is the point at which the shear properties are controlled, such as by use of a release layer or by use of adhesives in the complex laminates that have poor adhesion to the adjacent complex laminate. Control of the shear properties by use of a release layer or adhesives between complex laminates may be accomplished in a similar manner to that discussed above for the combination of two basic laminate layers.

[0039] The basic or complex laminates may also be provided with a protective layer on the outside of the outer fiber bundles to enhance durability, such as to resist moisture, wear, etc. This material is preferably a thin thermoplastic film or fabric, with, for example, a minimal thickness. Fabrics such as low denier (200 or less) nylon are preferred, and material such as polyethylene or urethane films with a thickness of less than 0.0005 mil are most preferred.

[0040] Also, the angles at which the first and second fiber bundle layers 10, 20 are disposed relative to each other may be varied without departing from the spirit and scope of the invention. For example, the first and second fiber bundle layers may be disposed at 45 degree angles relative to each other as opposed to the 90 degree angles illustrated in the Figures.

[0041] Variety of the angles within a complex laminate is also within the spirit and scope of the invention. For example, a complex laminate may be made up of four layers with the second layer disposed at a 90 degree angle to the bottom layer, the third layer disposed at a +45 degree angle relative to the bottom layer and the top layer disposed at a -45 degree angle relative to the bottom layer. And one or more complex laminates may be disposed in a single article.

[0042] In many applications, a single ply or set of two layers disposed at 90 degree angles relative to each other — (0, 90) — is preferred. For some applications, more than one ply or layer is preferable. Other variations include (0, 90, +45, -45)N — four layers disposed at the specified angles; N being a positive integer representing the number of plies or layer sets — or (0, -45, +45, 9O)N, etc.

[0043] The manner in which the fiber bundles are dispersed may vary widely. The fiber bundles may be aligned in a substantially parallel, unidirectional fashion, or fiber bundles may by aligned in a multidirectional fashion with fiber bundles at varying angles with each other. In the preferred embodiments of this invention, fiber bundles in each layer are aligned in a substantially parallel, unidirectional fashion such as in a prepreg, pultruded sheet and the like.

[0044] One such suitable arrangement is a complex laminate that includes a plurality of layers or laminates in which the fiber bundles are arranged in a sheet-like array and aligned parallel to one another along a common filament direction. Successive layers of such coated, unidirectional fiber bundles can be rotated with respect to the previous layer to form a relatively flexible composite. An example of such laminate structures are composites with the second, third, fourth and fifth layers rotated +45 degree, -45 degree, 90 degree and 0 degree, with respect to the first layer, but not necessarily in that order. Other examples include composites with 0 degree/90 degree layout of yarn or fiber bundles. Techniques and materials for fabricating these laminated structures are known.

[0045] To manufacture a laminate, an adhesive is applied to at least one side of a network or layer of fiber bundles. The fibers in the fiber bundle layer may be arranged in networks having various configurations. For example, a plurality of filaments can be grouped together to form twisted or untwisted yarn bundles in various alignments. The filaments or yarn may be formed as a felt, knitted or woven (plain, basket, satin and crow feet weaves, etc.) into a network, fabricated into non-woven fabric, arranged in parallel array, layered, or formed into a woven fabric by any of a variety of conventional techniques.

[0046] The adhesive layers may be applied in line with the use of a continuing laminating press and can be applied at the same time as the release layer. Generally, the present invention allows for lamination at relatively low pressures and still produce a durable laminate. A preferred pressure for lamination of the layers uses vacuum pressure of 14 psi to bond the layers of the laminate Higher processing pressures may be employed as long as the adhesive layer and/or release layer do not flow into and wet out the fiber.

[0047] The fibers believed to be suitable in the fabrication of the fiber bundles 12 vary widely and are, preferably, organic or inorganic fibers having a tensile strength of at least about 5 grams/denier, a tensile modulus of at least about 30 grams/denier and an energy-to- break of at least about 20 joules/gram. The tensile properties may be measured by an Instron Tensile Testing Machine by pulling a 10 in. (25.4 cm) length of fiber clamped in barrel clamps at a rate of 10 in./min. (25.4 cm/min). Preferred fibers are those having a tenacity equal to or greater than about 10 g/d, a tensile modulus equal to or greater than about 150 g/d, and an energy-to-break equal to or greater than about 8 joules/gram. Particularly preferred fibers are those having a tenacity equal to or greater than about 20 g/d, a tensile modulus equal to or greater than about 500 g/d and energy-to-break equal to or greater than about 30 joules/grams.

[0048] The invention includes embodiments in which the tenacity of the fibers is equal to or greater than about 25 g/d, the tensile modulus is equal to or greater than about 1000 g/d, and the energy-to-break is equal to or greater than about 35 joules/grams, and embodiments with a tenacity equal to or greater than about 30 g/d, the tensile modulus equal to or greater than about 1300 g/d and the energy-to-break equal to or greater than about 40 joules/grams.

[0049] The denier of the fiber may vary widely. In general, suitable fiber denier is believed to be equal to or less than about 4000. In some embodiments, fiber denier is from about 10 to about 4000, such as between about 10 to about 3000, for example, between about 10 and 1500 or between about 10 and 1000.

[0050] Useful inorganic fibers are believed to include S-glass fibers, E-glass fibers, carbon fibers, boron fibers, alumina fibers, zirconia-silica fibers, alumina-silica fibers and the like.

[0051] Illustrative of organic fibers believed to be suitable are those composed of thermosetting resins, thermoplastics polymers and mixture thereof such as polyesters, polyolefms, polyetheramides, fluoropolymers, polyethers, celluloses, phenolics, polyesteramides, polyurethanes, epoxies, aminoplastics, polysulfones, polyetherketones, polyetheretherketones, polyesterimides, polyphenylene sulfides, polyether acryl ketones, poly(amideimides), and polyimides. Illustrative of other useful organic fibers are those composed of aramids (aromatic polyamides), such as polyøn-xylylene adipamide), poly(p- xylylene sebacamide), poly 2,2,2-trimethylhexamethylene terephthalamide), ρoly(piperazine sebacamide), poly(metaphenylene isophthalamide) (Nomex®) and poly(p-phenylene terephthalamide) (Kevlar®); aliphatic and cyclo aliphatic polyamides, such as the copolyamide of 30% hexamethylene diammonium isophthalate and 70% hexamethylene diammonium adipate, the copolyamide of up to 30% bis-(-amidocyclohexyl)methylene, terephthalic acid and caprolactam, polyhexamethylene adipamide (nylon 66), poly(butyrolactam) (nylon 4), poly (9-aminonoanoic acid) (nylon 9), poly(enantholactam) (nylon 7), poly(capryllactam) (nylon 8), polycaprolactam (nylon 6), poly(p-phenylene terephthalamide), polyhexamethylene sebacamide (nylon 6,10), polyaminoundecanamide (nylon 11), polydodeconolactam (nylon 12), polyhexamethylene isophthalamide, polyhexamethylene terephthalamide, polycaproamide, poly(nonamethylene azelamide) (nylon 9,9), ρoly(decamethylene azelamide) (nylon 10,9), poly(decamethylene sebacamide) (nylon 10,10), poly>bis-(4-aminocyclothexyl)methane 1,10-decanedicarboxamide! (Qiana) (trans), or combination thereof; and aliphatic, cycloaliphatic and aromatic polyesters such as poly(l,4-cyclohexlidene dimethyl eneterephathalate) cis and trans, poly(ethylene-l,5- naphthalate), poly(ethylene-2,6-naphthalate), poly(l,4-cyclohexane dimethylene terephthalate) (trans), poly(decamethylene terephthalate), poly(ethylene terephthalate), poly(ethylene isophthalate), poly(ethylene oxybenozoate), poly(para-hydroxy benzoate), poly(dimethylpropio lactone), poly(decamethylene adipate), poly(ethylene succinate), poly(ethylene azelate), poly(decamethylene sebacate), poly(.beta.,.beta.-dimethyl- propiolactone), and the like.

[0052] Also illustrative of organic fibers believed useful are those of liquid crystalline polymers such as lyotropic liquid crystalline polymers which include polypeptides such as poly δ-benzyl L-glutamate and the like; aromatic polyamides such as ρoly(l,4-benzamide), poly(chloro-l,4-phenylene terephthalamide), poly(l,4-phenylene fumaramide), poly(chloro- 1,4-phenylene fumaramide), poly(4,4'-benzanilide trans, trans-muconamide), poly(l,4- phenylene mesaconamide), poly(l,4-phenylene) (trans- 1,4-cyclohexylene amide), poly(chloro-l,4-phenylene) (trans- 1,4-cyclohexylene amide), poly(l,4-phenylene 1,4- dimethyl-trans- 1,4-cyclohexylene amide), poly(l,4-ph.enylene 2.5-pyridine amide), poly(chloro-l,4-phenylene 2.5-pyridine amide), poly(3,3'-dimethyl-4,4'-biphenylene 2.5 pyridine amide), poly(l,4-phenylene 4,4'-stilbene amide), poly(chloro-l,4-phenylene 4,4'- stilbene amide), poly(l,4-phenylene 4,4'-azobenzene amide), poly(4,4'-azobenzene 4,4'- azobenzene amide), poly(l,4'-phenylene 4,4'-azoxybenzene amide), poly(4,4'-azobenzene 4,4'-azoxybenzene amide), poly(l,4-cyclohexylene 4,4'-azobenzene amide), poly(4,4'- azobenzene terephthal amide), poly(3.8-phenanthridinone terephthal amide), poly(4,4'- biphenylene terephthal amide), poly(4,4'-biphenylene 4,4'-bibenzo amide), poly(l,4- phenylene 4,4'-bibenzo amide), poly(l,4-phenylene 4,4'-terephenylene amide), poly(l,4- phenylene 2,6-naphthal amide), poly(l,5-naphthylene terephthal amide), poly(3,3'-dimethyl- 4,4-biphenylene terephthal amide), poly(3,3'-dimethoxy-4,4'-biphenylene terephthal amide), poly(3,3'-dimethoxy-4,4-biphenylene 4,4'-bibenzo amide) and the like; polyoxamides such as those derived from 2,2'dimethyl-4,4'dianiino biphenyl and chloro-l,4-phenylene diamine; polyhydrazides such as poly chloroterephthalic hydrazide, 2,5-pyridine dicarboxylic acid hydrazide) poly(terephthalic hydrazide), poly^erephthalic-chloroterephthalic hydrazide) and the like; poly(amide-hydrazides) such as poly(terephthaloyl 1,4 amino-benzhydrazide) and those prepared from 4-amino-benzhydrazide, oxalic dihydrazide, terephthalic dihydrazide and para-aromatic diacid chlorides; polyesters such as those of the compositions include poly(oxy-trans-l ^-cyclohexyleneoxycarbonyl-trans-l ,4-cyclohexylenecarbony l-/3-oxy- 1 ,4- phenyl-eneoxyterephthaloyl) and poly(oxy-cis- 1 ^-cyclohexyleneoxycarbonyl-trans- 1 ,4- cyclohexylenecarbonyl-jδ-oxy-l^-phenyleneoxyterephthaloyl) in methylene chloride-o-cresol poly>(oxy-trans-l,4-cyclohexylene-oxycarbonyl-trans-l,4-cyclohexylenecarbonyl-/3-oxy-(2- methyl- 1 ,4-phenylene)oxy-terephthaloyl) in 1 , 1 ,2,2-tetrachloroethane-o-chlorophenol-phenol (60:25 : 15 vol/vol/vol), poly-oxy-trans- 1 ^-cyclohexyleneoxycarbonyl-trans- 1 ,4- cyclohexylenecarbony l-/3-oxy(2-methyl-l,3-phenylene)oxy-terephthaloyl in o-chlorophenol and the like; polyazomethines such as those prepared from 4,4'-diaminobenzanilide and terephthalaldephide, methyl- 1,4-phenylenediamine and terephthalaldelyde and the like; polyisocyanides such as poly(-phenyl ethyl isocyanide), poly(n-octyl isocyanide) and the like; polyisocyanates such as poly(n-alkyl isocyanates) as for example poly(n-butyl isocyanate), poly(n-hexyl isocyanate) and the like; lyrotropic crystalline polymers with heterocylic units such as poly(l,4-phenylene-2,6-benzobisthiazole) (PBT), poly(l,4- phenylene-2,6-benzobisoxazole) (PBO), poly(l,4-phenylene-l,3,4-oxadiazole), poly(l,4- phenylene-2,6-benzobisimidazole), poly-2,5(6)-benzimidazole (AB-PBI), poly-2,6-(l,4- phneylene)-4-phenylquinoline, poly- 1 , 1 '-(4,4'-biphenylene)-6,6'-bis(4-phenylquinolme) and the like; polyorganophosphazines such as polyphosphazine, polybisphenoxyphosphazine, poly-bis(2,2,2'trifluoroethyelene)phosphazine and the like; metal polymers such as those derived by condensation of trans-bis(tri-n-butylphosphine)platinum dichloride with a bisacetylene or trans-bis(tri-n-butylphosphine)bis(l,4-butadinynyl)platinum and similar combinations in the presence of cuprous iodine and an amide; cellulose and cellulose derivatives such as esters of cellulose as for example triacetate cellulose, acetate cellulose, acetate-butyrate cellulose, nitrate cellulose, and sulfate cellulose, ethers of cellulose as for example, ethyl ether cellulose, hydroxymethyl ether cellulose, hydroxypropyl ether cellulose, carboxymethyl ether cellulose, ethyl hydroxyethyl ether cellulose, cyanoethylethyl ether cellulose, ether-esters of cellulose as for example acetoxyethyl ether cellulose and benzoyloxypropyl ether cellulose, and urethane cellulose as for example phenyl urethane cellulose; thermotropic liquid crystalline polymers such as celluloses and their derivatives as for example hydroxypropyl cellulose, ethyl cellulose propionoxypropyl cellulose, thermotropic liquid crystalline polymers such as celluloses and their derivatives as for example hydroxypropyl cellulose, ethyl cellulose propionoxypropyl cellulose; thermotropic copolyesters as for example copolymers of 6-hydroxy-2-naphthoic acid and p-hydroxy benzoic acid, copolymers of 6-hydroxy-2-naphthoic acid, terephthalic acid and p-amino phenol, copolymers of 6-hydroxy-2-naphthoic acid, terephthalic acid and hydroquinone, copolymers of 6-hydoroxy-2-naphtoic acid, p-hydroxy benzoic acid, hydroquinone and terephthalic acid, copolymers of 2,6-naphthalene dicarboxylic acid, terephthalic acid, isophthalic acid and hydroquinone, copolymers of 2,6-naphthalene dicarboxylic acid and terephthalic acid, copolymers of p-hydroxybenzoic acid, terephthalic acid and 4,4'- dihydoxydiphenyl, copolymers of p-hydroxybenzoic acid, terephthalic acid, isophthalic acid and 4,4'-dihydroxydiphenyl, p-hydroxybenzoic acid, isophthalic acid, hydroquinone and 4,4'- dihydroxybenzophenone, copolymers of phenylterephthalic acid and hydroquinone, copolymers of chlorohydroquinone, terephthalic acid and p-acetoxy cinnaniic acid, copolymers of chlorohydroquinone, terephthalic acid and ethylene dioxy-4,4'-dibenzoic acid, copolymers of hydroquinone, methylhydroquinone, p-hydroxybenzoic acid and isophthalic acid, copolymers of (l-phenylethyl)hydroquinone, terephthalic acid and hydroquinone, and copolymers of poly(ethylene terephthalate) and p-hydroxybenzoic acid; and thermotropic polyamides and thermotropic copoly(amide-esters).

[0053] Also illustrative of organic fibers believed to be useful in the fabrication of fiber bundles 12 are those composed of extended chain polymers formed by polymerization of α, β-unsaturated monomers of the formula¹.

R₁ R₂ -C=CH₂

wherein:

Ri and R₂ are the same or different and are hydrogen, hydroxy, halogen, alkylcarbonyl, carboxy, alkoxycarbonyl, heterocycle or alkyl or aryl either unsubstituted or substituted with one or more substituents selected from the group consisting of alkoxy, cyano, hydroxy, alkyl and aryl. Illustrative of such polymers of a, β-unsaturated monomers are polymers including polystyrene, polyethylene, polypropylene, poly(l-octadence), polyisobutylene, poly(l- pentene), poly(2-methylstyrene), poly(4-methylstyrene), poly(l-hexene), ρoly(l-pentene), poly(4-methoxystrene), poly(5-methyl-l-hexene), poly(4-methylpentene), poly(l-butene), polyvinyl chloride, polybutylene, polyacrylonitrile, poly(methyl pantene-1), poly(vinyl alcohol), poly(vinyl-acetate), polyvinyl butyral), poly(vinyl chloride), poly(vinylidene chloride), vinyl chloride-vinyl acetate chloride copolymer, poly(vinylidene fluoride), poly(methyl acrylate, poly(methyl methacrylate), poly(methacrylo-nitrile), poly(acrylamide), polyvinyl fluoride), polyvinyl formal), poly(3 -methyl- 1-butene), poly(l-pentene), poly(4- methyl-1-butene), poly(l-pentene), poly(4-methyl-l-pentence, poly(l-hexane), poly(5-methyl- 1-hexene), poly(l-octadence), poly(vinyl-cyclopentane), poly(vinylcyclothexane), poly(a- vinyl-naphthalene), polyvinyl methyl ether), poly(vinyl-ethylether), polyvinyl propylether), poly(vinyl carbazole), polyvinyl pyrolidone), poly(2-chlorostyrene), poly(4-chlorostyrene), poly(vinyl formate), poly(vinyl butyl ether), poly(vinyl octyl ether), poly(vinyl methyl ketone), poly(methyl-isopropenyl ketone), pσly(4-phenylstyrene) and the like.

[0054] In some embodiments, composite articles include a fiber network, which may include a high molecular weight polyethylene fiber, a high molecular weight polypropylene fiber, an aramide fiber, a high molecular weight polyvinyl alcohol fiber, a high molecular weight polyacrylonitrile fiber or mixtures thereof. In the case of polyethylene, suitable fibers are believed to be those of molecular weight of at least 150,000, preferably at least one million and more preferably between two million and five million. Such extended chain polyethylene (ECPE) fibers may be grown in solution, or a filament spun from a solution to form a gel structure, as is known. As used herein, the term polyethylene shall mean a predominantly linear polyethylene 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 wt % of one or more polymeric additives such as alkene-1 -polymers, in particular low density polyethylene, polypropylene or polybutylene, copolymers containing mono-olefins as primary monomers, oxidized poryolefϊns, graft polyolefm copolymers and polyoxymetliylenes, or low molecular weight additives such as anti-oxidants, lubricants, ultra-violet screening agents, colorants and the like which are commonly incorporated by reference. Depending upon the formation technique, the draw ratio and temperatures, and other conditions, a variety of properties can be imparted to these fibers.

[0055] Similarly, highly oriented polypropylene fibers of molecular weight at least 200,000, preferably at least one million and more preferably at least two million may be used. Such high molecular weight polypropylene may be formed into reasonably well oriented fibers by the techniques known. Since polypropylene is a much less crystalline material than polyethylene and contains pendant methyl groups, tenacity values achievable with polypropylene are generally substantially lower than the corresponding values for polyethylene. Accordingly, a suitable tenacity is at least S grams/denier, with a preferred tenacity being at least 11 grams/denier. The tensile modulus (as measured by an Instron Tensile Testing Machine) for polypropylene is at least 160 grams/denier, preferably at least 200 grams/denier. The particularly preferred ranges for the above-described parameters can advantageously provide improved performance in the final article.

[0056] High molecular weight polyvinyl alcohol fibers having high tensile modulus are believed suitable for the present invention. In the case of polyvinyl alcohol (PV-OH), PV-OH fiber of molecular weight of at least about 200,000 may be particularly suitable. Particularly useful PV-OH fiber preferably has a tensile modulus (as measured by an Instron Tensile Testing Machine) of at least about 300 g/d, a tenacity of at least 7 g/d (preferably at least about 10 g/d, more preferably at about 14 g/d, and most preferably at least about 17 g/d), and an energy-to-break of at least about 8 joules/gram. PV-OH filaments having a weight average molecular weight of at least about 200,000, a tenacity of at least about 10 g/d, a tensile modulus (as measured by an Instron Tensile Testing Machine) of at least about 300 g/d, and an energy-to-break of about 8 joules/gram may be more useful in producing a ballistic resistant article. PV-OH fiber having such properties can be produced by known methods.

[0057] Polyacrylonitrile (PAN) fiber of molecular weight of at least about 400,000 is believed to be suitable. Particularly useful PAN filament should have a tenacity of at least about 10 g/d (as measured by an Instron Tensile Testing Machine) and an energy-to-break of at least about 8 joules/gram. PAN fiber having a molecular weight of at least about 400,000, a tenacity of at least about 15 to about 20 g/d and an energy-to-break of at least 8 joules/gram is most useful in producing ballistic resistant articles.

[0058] In the case of aramid fibers, suitable aramid fibers formed principally from aromatic polyamide are known. Preferred aramid fiber will have a tenacity of at least about 20 g/d (as measured by an Instron Tensile Testing Machine), a tensile modulus of at least about 400 g/d (as measured by an Instron Tensile Testing Machine) and an energy-to-break at least about 8 joules/gram, and particularly preferred aramid fibers will have a tenacity of at least about 20 g/d, a modulus of at least about 4SO g/d and an energy-to-break of at least about 20 joules/gram. Most preferred aramid fibers will have a tenacity of at least about 20 g/denier, a modulus of at least about 900 g/denier and an energy-to-break of at least about 30 joules/gram. For example, poly(phenylene terephthalamide) fibers produced commercially by Dupont Corporation under the trade name of Kevlar® 29, 49, 129 and 149 having moderately high modulus and tenacity values are believed particularly useful in forming ballistic resistant composites. Also believed useful in the practice of this invention is poly(metaphenylene isophthalamide) fibers produced commercially by Dupont under the tradename Nomex®.

[0059] In the case of liquid crystal copolyesters, suitable fibers are known. Tenacities of about 15 to about 30 g/d (as measured by an histron Tensile Testing Machine) and preferably about 20 to about 25 g/d, and tensile modulus of about 500 to 1500 g/d (as measured by an histron Tensile Testing Machine) and preferably about 1000 to about 1200 g/d are particularly desirable. Fibers made under the trade name Vectran®, by Celanese corporation are believed very suitable. Preferred fibers for use in the fiber network are Vectran LCP, and PBO fibers. More preferred are aramid fibers sold under the trade name Kevlar® and Twaron®, and most preferred fibers are high performance polyethylene sold under the trade names Spectra® (Honeywell) and Dyneema® (DSM Corporation).

[0060] The adhesive layer can be made of any number of suitable polymeric adhesives. The adhesive can be of a thermosetting or thermoplastic type. Preferred adhesives believed suitable include polydienes such as polybutadiene, polychloroprene and polysioprene; olefinic and copolymers such as ethylene-propylene, ethylene-chloropylene-diene copolymers, isobutylene-soprene copolymer, and chlorosulfonated polyethylene; natural rubber, polyfulfides, polyurethane elastomers; polyacrylates; polyethers; fluoroelastomer; unsaturated polyesters; vinyl esters; alkyds; flexible epoxy, flexible polyamides; epichlorophydrin; polyvinyls; flexible phenolics; silcon eleastomers; thermoplastic elastomers; copolymers of ethylene, polyvinyl formal, polyvinyl butyal; and poly(bis- maleimide). Blends of any combination of one or more of the above-mentioned adhesive materials are also believed suitable.

[0061] Most preferred adhesives are polybutadiene, polyisoprene, natural rubber, ethylene- propylene copolymers, ethylene-propylene-diene terpolymers, polysulfides, polyurethane elastomers, chlorosulfonated polyethylene, polychloroprene, poly(isobutyleneco-isoρrene), polyacrylates, polyesters, vinyl esters, flexible epoxy, flexible nylon, silicone elastomers, copolymers of ethylene, polyvinyl formal, polyvinyl butyral, and blends of and combinations of two or more of the above-mentioned adhesive materials.

[0062] The adhesive material is, for example, a low modulus, elastomeric material which has a tensile modulus, measured at about 23° C, of less than about 80,000 psi, for example, less than about 50,000 psi. For example, the tensile modulus is between about 7,000 psi and about 80,000 psi. The elastomeric material preferably has an elongation to break of at least about 5%. Preferably, the elongation to break of the elastomeric material is at least about 30%, more preferably is at least about 50%, and most preferably is at least about 100%. Representative examples of materials believed suitable for use as a flexible adhesive are block copolymers of conjugated dienes such as butadiene and isoprene, and vinyl aromatic monomers such as styrene, vinyl toluene and t-butyl styrene; polydienes such as polybutadiene and polychloroprene, polyisoprene; natural rubber; copolymers and polymers of olefins and dienes such as ethylene-propylene copolymers, ethylene-propylene-diene terpolymers and poly(isobutylene-co-isoprene), polyfulfide polymers, polyurethane elastomers, and chlorosulfonated polyethylene; pasticized polyvinylchloride using dioctyl phthate or other plasticizers well known in the art; butadiene acrylonitrile elastomers; polyacrylates such as ρoly(acrylic acid), poly(methylcyanoacrylate), poly(methylacrylate), poly(ethyl acrylate), poly(propylacrylate), poly(methylacrylonitrile), poly(acrylamide), poly(N-isopropylacrylamide) and the like, polyesters; polyethers; fluoroelastomers; poly(bismaleimide); flexible epoxies; flexible phenolics; polyurethanes; silicone elastomers; flexible polyamides; unsaturated polyesters; vinyl easters, polyolefins, such as polybutylene and polyethylene; polyvinyls such as poly(vinyl formate), poly(vinylbenzoate), poly(vinyl- carbazole), poly(vinylmethylketone), poly(vinyl-methyl ether), polyvinyl acetate, polyvinyl butyral, and poly( vinyl formal); and polyolefinic elastomers.

[0063] One form for the adhesive is a non-woven spun thermoplastic adhesive. Examples of these polymeric materials are sold under the trade name SpunFab®, by Spunfab Corporation, Cuyahoga Falls, Ohio, and under the trade name Sharenet®, by Bostik Corporation, Middleton, MA. The preferred adhesives are Spunfab® Ternary Resins, more preferred are polyamides and polyesters, and most preferred are EAV and polyolefins.

[0064] The release layer can be any suitable material that provides at least about 15% reduction in the interlaminar shear strength between the layers, as defined by the clinging drum peel test in ASTM D1781-98 (2004), compared to a laminate without such a release layer. Suitable materials include paper, metal foil, or plastic film. More preferable are plastic films such as polyester, polypropylene or urethane. Even more preferable are polyethylene films with an areal weight less than 50 grams per sq meter, and most preferable are polyethylene films with an areal weight less than 8 grams per sq meter. Lower inter- laminar shear can also be obtained with the application of a release agent such as silicone to the release film or the adhesive layer prior to bonding. This approach allows tailoring the inter-laminar shear to meet a specific ballistic requirement.

[0065] The articles of this invention can be fabricated using a number of procedures. In general, layers are formed by molding the combination of the fiber bundles in the desired configurations and amounts by subjecting the combination to heat and pressure during a mold cycle time. The molding temperature is usually selected such that it is less than the melting or softening point of the polymer from which the fibers of the fiber bundle layer are formed or the temperature at which fiber damage occurs, but is greater than the melting point or softening point of the polymer or polymers forming release or adhesive layer(s). For example, for extended chain polyethylene filaments, molding temperatures range from about 20° to about 150° C, preferably from about 80° to about 145° C, and more preferably from about 100° to about 135° C. The molding pressure may vary widely and preferably may range from about 10 psi (69 IcPa) to about 30,000 psi (207,000 IcPa). A pressure between about 10 psi (69 IcPa) and about 100 psi (690 kPa), when combined with temperatures above about 100° C for a period of time less than about 1.0 minute, maybe used simply to cause the fibrous layers and polymeric adhesive layers to stick together. A combination of pressure and temperature that would result in the adhesive layer and/or release layer impregnating into the fibers to form a resin matrix is preferably avoided.

[0066] For fibers such as aramid and Vectran® LCP, molding temperatures can approach 250° C, and the limiting factor is the temperature capability of the adhesive and the release layer, which will vary greatly depending on the particular material.

[0067] The SAPI (small arms protective insert) application is a good example of where this material can be utilized in conjunction with ceramic materials to defeat multiple threats. This invention can be incorporated as a backing to a ceramic facing and. is very suitable for this application. [0068] Another useful embodiment of the invention is as a soft armor material in ballistic vests. Because the material of the present invention is bonded with an adhesive layer as opposed to a non-adhesive film layer, the structural integrity of the flexible product is greatly enhanced. The benefit is more durability during long term use.

[0069] Figure 6 illustrates a preferred embodiment for soft armor. In this embodiment, the preferred unidirectional fiber bundles are coated with adhesive on both outer surfaces of the fiber bundles, and the release layer is laminated to one of the adhesive layers. The material is then cross plied (0/90) at a 90 degree orientation with a similar layer. The two layers are laminated under heat and pressure. The number of [0,90] layers is generally less than 5 and more preferably less than three. The orientation between layers can vary, with each layer at some angle to the other, for example, [0,90], [0,90,-45,45], [-45,45,-45,45], etc., as discussed above. There are endless combinations that are within the scope of the invention.

[0070] Other forms of the complex composite which are believed useful in this invention are, for example, a composite comprising multiple alternating layers of composite laminate and rigid layer.

[0071] The rigid layers preferably include an impact resistant material, such as solid or perforated steel plate or other metallic material, composite aπnor plate, ceramic material, ceramic reinforced metallic composite, and high strength fiber composites (for example, an aramid fiber and a high modulus, resin matrix such as epoxy or phenolic resin vinyl ester, unsaturated polyester, thermoplastics, nylon 6, nylon 6, 6 and polyvinylidine halides.) The ceramic is, for example, a carbide, such as boron carbide or silicon carbide, an oxide, such as aluminum oxide, or a nitride, such as silicon nitride. Other ceramic materials are also suitable for use. Most preferably, the rigid impact resistant layer is one that is ballistically effective.

[0072] Surprisingly, the inclusion of an adhesive layer between the release layer or film and the fiber bundles, without penetration of the adhesive substantially into the fiber bundles or through the laminate from one side to the other, increases ballistic performance over structures that do not have such an adhesive. Laminates made and tested with only the adhesive layer tended to perform lower in ballistic testing. Facilitating this release with adhesives layer alone, however, can also be achieved with the use of different adhesive layers, both which bond to the fiber substrates, but which are not well suited to bonded to each other.

[0073] ^"Without intending to be bound to any particular theory, it is possible that the improved adhesion between the fiber bundles achieved by use of the adhesive that does not substantially penetrate into the fiber bundle allows for better energy distribution within the layer in the laminate upon ballistic impact, resulting in better ballistic performance. The release or film layer of the present invention is not the sole adhesion layer among fibers of the fiber bundles, but helps minimize inter-laminar shear strength during ballistic impact. Reducing inter-laminar shear strength is believed to help the panels or layers delaminate and absorb energy during the ballistic event.

[0074] Utilizing an adhesive layer that is optimized for adhesion also improves the durability of the overall laminate structure, especially when used a dual layer soft armor product.

EXAMPLES

[0075] In one example, laminates were made with Spunfab^® adhesive POX 80579G (0.25 oz/ square yard) as the adhesive layer and 0.0035 inch thick polyethylene film as the release layer. Laminates were made with 80% fiber content with the resin being made of (A) a release layer next to an adhesive layer next to the fiber layer, and (B) an adhesive layer next to the fiber layer, with no release layer. They were tested to the NIJ (National Institute of Justice) .08 standard against an M-80 ball round and a V50 penetration velocity was determined. The material with the release layer out-performed the material with adhesive alone, as shown in Table 1.

Table 1— Ballistic testing on M-80 ball round

[0076] This is a surprising result because it is generally considered in the industry that the addition of resin materials are parasitic and do not affect the ballistic properties. The fact that the ballistic properties can be affected by how this parasitic weight is added is surprising.

[0077] Test plates were made using aluminum oxide ceramic (0.195 inch thick) and a backing of Kevlar^® aramid fibers using Spunfab^® 80410 adhesive (0.25 oz/sq yard) on each side of a uni-directional Kevlar^® fibers, with a release layer of polyethylene. Samples were made to meet the specified weight of a heavyweight SAPI plate specification, and subjected to the first article ballistic testing as required by the U.S Army. The material passed all tests, demonstrating its suitability for use as a backing to ceramic.

[0078] Test panels were made to demonstrate the materials suitability against 9mm handgun threats. A 15"xl5" panel, 28 plies of uni-directional Kevlar^® fibers with Spunfab^® 80410 adhesive (0.25 oz/sq yard) on each side of the fibers, and a release layer of polyethylene were fabricated using a vacuum bag process (14psi) and subsequently tested against 9mm rounds. The resulting V50 of 1750 ft/sec was well in excess of NIJ requirement demonstrating suitability for use as armor for defeating handgun threats.

[0079] While the present invention has been illustrated by the above description of embodiments, and while the embodiments have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the invention to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and descried. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general or inventive concept.

Claims

I claim:

1. A laminate sheet for use in a ballistic structure, comprising at least one layer of unidirectionally-oriented fiber bundles and a discontinuous array of adhesive applied to at least one surface of the sheet without substantial penetration of the adhesive into the fiber bundles, wherein the discontinuous array of adhesive binds the fibers bundles together.

2. The laminate sheet of claim 1, wherein the adhesive comprises no more than about 20 percent by weight of the laminate sheet.

3. The laminate sheet of claim 2, wherein the adhesive comprises no more than about 12 percent by weight of the laminate sheet.

4. The laminate sheet of claim 1, wherein the adhesive has a tensile modulus between about 7,000 psi and about 80,000 psi.

5. The laminate sheet of claim 1, wherein the adhesive is a non- woven array of thermoplastic material.

6. The laminate sheet of claim 1, further comprising at least a first and a second layer of unidirectionally-oriented fiber bundles, wherein the second layer is oriented at an angle between 0 and 180 degrees relative to the first layer.

7. The laminate sheet of claim 1, further comprising a plurality of unidirectionally-oriented fiber bundles, wherein at least one of the layers is oriented at an angle between 0 and 180 degrees relative to at least one other layer.

8. The laminate sheet of claim 1, wherein the unidirectionally-oriented fiber bundles comprise fibers selected from the group consisting of nylon, polypropylene, polyethylene, aramid, and liquid crystalline polymer.

9. The laminate sheet of claim 6, further comprising at least one release layer disposed between the first and second layer, the release layer comprising plastic film, metal foil, or paper.

10. A laminate sheet for use in a ballistic structure, comprising:

a. at least a first layer of fiber bundles having a first adhesive associated therewith;

b. at least a second layer of fiber bundles laminated to the first layer and oriented at an angle between 0 and 180 degrees relative to the first layer; and

c. means for reducing the inter-laminar shear strength between the first layer and the second layer.

11. The laminate sheet of claim 10, wherein the first adhesive is applied to one or more surfaces of the first layer and does not substantially penetrate into the fiber bundles of the first layer.

12. The laminate sheet of claim 10, wherein the means for reducing inter-laminar shear strength comprises a release layer disposed between the first layer and the second layer.

13. The laminate sheet of claim 12, wherein the release layer comprises polyester film, polypropylene film, polyethylene film, urethane film, aluminum foil, steel foil, titanium foil, brass foil, copper foil, or paper.

14. The laminate sheet of claim 12, wherein the first adhesive is disposed between the release layer and the first layer.

15. The laminate sheet of claim 10, further comprising a second adhesive applied to one or more surfaces of the second layer and that does not substantially penetrate into the fiber bundles of the second layer.

16. The laminate sheet of claim 15, wherein the second adhesive is disposed between the release layer and the second layer.

17. The laminate sheet of claim 15, wherein the means for reducing the inter- laminar shear strength between the first layer and the second layer comprises selecting the first adhesive and the second adhesive such that there is relatively low bonding affinity therebetween, and such that localized de-bonding between the first layer and the second layer occurs at a point of ballistic impact.

18. The laminate sheet of claim 10, wherein the first layer and the second layer are oriented at non-zero angle relative to each other.

19. The laminate sheet of claim 10, further comprising more than two layers of fiber bundles and means for reducing the inter-laminar shear strength between selected layers.

20. A laminate sheet for use in a ballistic structure comprising:

a. a first layer of unidirectionally-oriented fiber bundles;

b. a second layer of unidirectionally-oriented fiber bundles laminated to the first layer and oriented at an angle of between 0 and 180 degrees relative to the first layer;

c. a release layer disposed between the first layer and the second layer; and

d. a first adhesive disposed between the release layer and the first layer;

wherein the release layer has relatively low bonding affinity for the first adhesive, such that localized debonding between the first layer and the second layer occurs at the point of ballistic impact.

21. The laminate sheet of claim 20, further comprising a second adhesive between the release layer and the second layer.

22. The laminate sheet of claim 21, wherein the first adhesive and the second adhesive are substantially the same material.

23. The laminate sheet of claim 21, wherein the first adhesive and the second adhesive are different materials.

24. The laminate sheet of claim 20, further comprising additional layers of unidirectionally-oriented fiber bundles oriented at angles between 0 and 180 degrees relative to other layers, each additional layer comprising at least one adhesive layer, at least one release layer, or both.

25. A ballistic structure comprising the laminate sheet of claim 20.

26. A laminate sheet for use in a ballistic structure comprising

a. a plurality of complex laminates laminated together, each complex laminate oriented at an angle between 0 and 180 degrees relative to at least one other complex laminate; each complex laminate comprising a plurality of laminated layers of unidirectionally-oriented fiber bundles, each layer oriented at an angle between 0 and 180 degrees relative to at least one other layer;

b. means for reducing the inter-laminar shear strength between selected laminated layers; and

c. means for reducing the inter-laminar shear strength between selected complex laminates.

27. The laminate sheet of claim 26, wherein the means for reducing inter-laminar shear strength between selected complex laminates comprises a release layer disposed between selected complex laminates.

28. The laminate sheet of claim 27, further comprising an adhesive layer disposed on at least one surface of the release layer.

29. The laminate sheet of claim 28, wherein the adhesive layer comprises a non- woven array of thermoplastic material.

30. The laminate sheet of claim 27, wherein the release layer comprises a polyethylene film having a thickness less than about 2 mil.

31. The laminate sheet of claim 26, wherein the unidirectionally-oriented fiber bundles comprise fibers selected from the group consisting of nylon, polypropylene, polyethylene, aramid, and liquid crystalline polymer.

32. A ballistic structure comprising at least one laminate sheet, the laminate sheet comprising:

a. a first layer of fiber bundles having a first adhesive on a surface thereof;

b. a second layer of fiber bundles laminated to the first layer; and

33. The ballistic structure of claim 32, further comprising at least one rigid impact resistant layer.

34. The ballistic structure of claim 33, wherein the rigid impact resistant layer comprises ceramic, metallic, perforated metallic, or composite material.

35. The ballistic structure of claim 33, wherein the rigid impact resistant layer is bonded to at least one laminate sheet.

36. The ballistic structure of claim 32, wherein the fiber bundles comprise fibers selected from the group consisting of nylon, polypropylene, polyethylene, aramid, and liquid crystalline polymer.

37. The ballistic structure of claim 32, wherein the adhesive comprises a non- woven array of thermoplastic material.