MX2007008028A - Moisture-resistant pbo fiber and articles, and method of making. - Google Patents

Abstract

PBO fibers, PBO fiber-containing sheets and assemblies thereof, having improved of properties after exposure to high humidity.The PBO fibers are encapsulated by anhydrous means in a sealant material having a water vapor permeasbility of less than 25x10^-11cm³(stp) cm/(cm² sec.Pa) as measured by ASTM E 96-95 (Procedure E) at 37.8 degree C, Inn the case of PBO fiber-containing sheets, the sealant material partially fills volume between the fibers.

Description

PBO FIBER RESISTANT TO MOISTURE AND ARTICLES AND MANUFACTURING METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to PBO fibers, fiber sheets comprising PBO fibers and mounts thereof having improved retention of properties after exposure to high humidity. These fibers, sheets and articles are useful in applications that require impact absorption, ballistic resistance and penetration resistance, as well as in other applications. 2. Description of the Related Art The production of high strength fibers from materials such as aramides, high molecular weight polyethylene (HMWPE) and, more recently, polybenzezoles (PBO), has made possible and practical the satisfaction of a broad range of needs. Perhaps more dramatically, the body armor constructed from these fibers has saved the lives of many of our police officers and military personnel. Body armor is typically constructed of layers of woven fabrics or non-woven sheets of fibers that are piled together. The fibers in a non-woven sheet can be oriented unidirectionally or caked in a random orientation. Unidirectional fiber sheets (UD sheets) usually contain a matrix resin that fills the volume between the fibers. The successive UD sheets are rotated in a mutual relationship, for example, at angles of 0 ° / 90 ° or 0 ° / 45 ° / 90 ° / 45 ° / 0 or at other angles. Compounds manufactured from cross-folded UD sheets, usually have better ballistic resistance than woven fabrics, and therefore have a weight advantage. Compounds with useful ballistic resistance can also be built for applications such as riot shields and helicopter seats, where individual sheets are adhered using heat and pressure to adhere the matrix to each sheet, forming a union between them, and consolidating the assembly into a unitary article. With respect to the current commercially available high strength fibers, PBO fibers have high strength and tensile modulus, both of which are important for propagating and distributing the voltage wave involved in a ballistic event. Unfortunately, however, PBO fibers can be weakened by exposure to high humidity (water in the vapor phase) with the consequent deterioration of their antiballistic effectiveness. A publication entitled "PBO Fiber ZYLON® Technical Information (Revised 9/2001) Toyobo Co. LTD., Shows that the PBO fibers, after an accelerated aging of six weeks at 70 ° C, 80% relative humidity, lose approximately 25% of their resistance. Frequently he wants a body armor to have a sufficient "breathability", that is, permeability to water vapor, to give an added level of comfort to the user. The construction of body armor from PBO fibers may therefore require addressing two conflicting problems: protecting the PBO fibers against the effects of moisture while simultaneously providing permeability to water vapor through the shield, for the user comfort. Articles with ballistic resistance and / or penetration resistant, comprising knitted fibers of PBO are known in the prior art. See, for example, US Pat. Nos. 6,559,079, 6,449,769, 6,238,768 and 5,552,221. These prior techniques, individually or in combination, do not describe the specific constructions of the articles or methods of this invention and do not meet all the needs gathered by this invention. BRIEF DESCRIPTION OF THE INVENTION The present invention comprises a method for manufacturing PBO fibers and sheets containing PBO fibers, as well as assemblies thereof, which have improved retention of their Properties after exposure to high humidity and temperature. These fibers, blades and mounts are useful in applications that require impact absorption, ballistic resistance and penetration resistance, as well as other applications. In one embodiment, the invention is a method for manufacturing PBO fibers resistant to the effects of heat and moisture, comprising the step of encapsulating the PBO fibers in a sealing material by anhydrous means. The sealing material has a water vapor permeability of less than 25x1o "11 cm3 (stp) • cm / (cm2 • sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C. can be manufactured in a variety of other articles In another embodiment, the invention is a method for constructing sheets, composed of PBO fibers and resistant to the effects of heat and humidity, comprising the steps of: a) building a sheet fibrous comprising a plurality of PBO fibers in a fibrous network; b) encapsulate the PBO fibers in a sealing material by anhydrous means, the sealing material having a water vapor permeability of less than 25x1o "11 cm3 (stp) -cm / (cm2 -sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C, the sealing material partially fills the volume between the fibers, and in the case of a network of non-woven fibers, additionally adheres the fibers; and c) optionally adhering a plastic film to at least one face of the fibrous sheet. In yet another embodiment, the invention is a method for constructing ballistic resistant articles that retains at least 87% of its initial V50 rating against a Geco 9 mm, 124 grain, FMJ (steel sheath) bullet after accelerated aging for four weeks at 70 ° C, 80% relative humidity, comprising the steps of: a) building a fibrous sheet comprising PBO fibers in a fibrous web, b) encapsulating the PBO fibers in a sealing material by anhydrous media, the material Seal that has a water vapor permeability of less than 25X10"11 cm3 (stp) -cm / (cm2 • sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C, the material of sealing that partially fills the volume between the fibers, and in the case of a network of non-woven fibers, which additionally adheres the fibers c) optionally adhering a plastic film to at least one face of the fibrous sheet; d) stacking a plurality of fibrous sheets one on top of the other in a decoupled or weakly coupled array. In another embodiment, the invention is a method for constructing items with ballistic resistance that retain at least 87% of their initial V50 rating against Geco 9mm, 124 grain, FMJ (steel deck) bullets after accelerated aging for four weeks at 70 °. C, relative humidity of 80%, comprising the steps of: a) aligning a plurality of PBO fibers in a unidirectional planar sheet; b) encapsulate the PBO fibers in a sealing material by anhydrous media, the sealing material having a water vapor permeability of less than 25x1o "11 cm3 (stp) • cm / (cm2 • sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C, the sealing material partially filling the volume between the fibers, and adhering the fibers to form a coherent sheet, c) stacking a first and a second of the sheets coherent one over the other, the direction of the fibers in the first sheet that is at an angle of at least 30 ° compared to the direction of the fibers in the second sheet, d) joining the first and second coherent sheets together to form a laminate; e) optionally adhering a plastic film to at least one face of the laminate and f) stacking a plurality of laminates on one another in a decoupled or weakly coupled arrangement. In another embodiment, the invention comprises PBO fibers, fibrous sheets and articles composed of one or more fibrous sheets composed of PBO fibers in a fibrous web. In each of these, the PBO fibers are encapsulated in a sealing material, as described above. Fibrous sheets may be formed from encapsulated PBO fibers or may be formed from PBO fibers and subsequently encapsulated. In the latter, the fibrous sheets subsequently encapsulated, the sealing material partially fills the volume between the fibers, and in the case of the non-woven sheets, the sealing material additionally adheres the fibers. The invention also includes assemblies of these articles. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic representation of a process for manufacturing a sheet of unidirectional PBO fibers of the invention. DETAILED DESCRIPTION OF THE INVENTION In one embodiment, the invention is a method for forming PBO fibers resistant to the effects of heat and moisture, comprising the step of encapsulating the PBO fibers in a sealing material by anhydrous means. The sealing material has a water vapor permeability of less than 25 x 10"11 cm3 (stp) -cm / (cm2-sec-Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C. In another embodiment, the invention is a method for constructing sheets, composed of PBO fibers and resistant to the effects of heat and moisture, comprising the steps of: a) building a fibrous sheet comprising PBO fibers in a fibrous network; b) encapsulate the PBO fibers in a sealing material by anhydrous means, the sealing material having a water vapor permeability of less than 25x1o "11 cm3 (stp) -cm / (cm2-sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C, c) partially fill the volume between the fibers with 1 sealing material, and c) optionally adhere a plastic film to at least one side of the fibrous sheet. embodiment, the invention is a method for constructing a ballistic resistant article that retains at least 87% of its initial V50 rating against Geco 9 mm, 124 grain, FMJ (steel deck) bullets after the accelerated aging for four weeks at 70 ° C, relative humidity of 80%, comprising the steps of: a) constructing a fibrous sheet comprising PBO fibers in a re fibrous, - b) encapsulating the PBO fibers in a material of sealed by anhydrous media, the sealing material having a water vapor permeability of less than 25x1o "11 cm3 (stp) • cm / (cm2 • sec- Pa) when measured by ASTM E 96-95 (Procedure E) a 37.8 ° C, the sealing material that partially fills the volume between the fibers, and in the case of a non-woven fibrous web, which additionally adheres the fibers, c) optionally adhere a plastic film to at least one side of the fibrous sheet and d) stacking a plurality of fibrous sheets on one another in a decoupled or weakly coupled arrangement In other embodiments, the invention is a method for constructing ballistically resistant articles that retain at least 87% of their initial V50 rating against Geco 9mm bullets 124 g FMJ (steel cover) after accelerated aging for four weeks at 70 ° C, relative humidity of 80%, comprising the steps of: a) aligning a plurality of PBO fibers in a unidirectional flat sheet; b) encapsulate the PBO fibers in a sealing material by anhydrous media, the sealing material having a vapor permeability of less than 25x10"13" cm3 (stp) -cm / (cm2 • sec-a) when measured by ASTM E 96-95 (Method E) at 37.8 ° C, the sealing material that partially fills the volume between the fibers and that additionally adheres the fibers to form a coherent sheet; c) stacking a first and a second of the coherent sheets one on top of the other, the direction of the fibers in the first sheet that is at an angle of at least 30 ° compared to the direction of the fibers in the second sheet; d) joining the first and second coherent sheets to form a laminate; e) optionally adhering a plastic film to one or both sides of the laminate; and f) stacking a plurality of laminates on one another in a decoupled or weakly coupled array. In other embodiments, the invention comprises fibers, fibrous sheets, and articles composed of one or more fibrous sheets composed of PBO fibers in a fibrous web. Fibers and / or fibrous sheets are encapsulated in the sealing material previously described. In the case of fibrous sheets, the sealing material partially fills the volume between the fibers, in the case of the non-woven sheets, additionally adheres the fibers. The invention also includes assemblies of these articles. For the purposes of the present invention, a fiber is an elongated body, the length dimension of which is much greater than the transverse dimensions of width and thickness. Accordingly, "fiber" as used herein includes, one, or a plurality of filaments, tapes, strips, and the like having regular or irregular cross sections in continuous or discontinuous lengths. A yarn is an aggregate of continuous or discontinuous fibers. As used herein, "fibrous web" or "network" denotes a plurality of fibers disposed in a predetermined configuration, or a plurality of fibers grouped together to form a twisted or unbent yarn, which yarns are arranged in a predetermined configuration. The fiber network can have several configurations. For example, fibers or yarn may be constructed as a fleece, warping, braiding, weaving, a non-woven oriented randomly, a non-woven oriented unidirectionally, or formed in a network by any of the conventional techniques. According to a particularly preferred network configuration, the fibers are aligned unidirectionally so that they are substantially parallel to each other along the longitudinal direction of the network layer. The sheets and articles of the invention can be further composed of other high strength fibers, such as high molecular weight polyethylene (HMPE), aramides and liquid crystal polyesters. When used in conjunction with the PBO fibers in unidirectional orientation of the fibers, as preferred, these fibers are aligned parallel to the PBO fibers. It is also preferred that the fibers of different compositions are arranged in an essentially periodic arrangement in a direction transverse to the direction of the fibers. The sheet arti containing hybrid fibers of the present invention are preferably composed of from 10 to 100 percent PBO fibers based on the total fiber pitch. The PBO fibers in the context of this invention are polybenzazole or polybenzoxazole fibers. PBO fibers suitable for the practice of this invention have been described, for example, in U.S. Patents 5,185,296, 5,286,833, 5,356,584, 5,534,205, 5,976,447 and 6,040,050, incorporated herein by reference. Preferably, the PBO fibers are poly (p-phenylene-2,6-benzobisoxazole) fibers of the trademark ZYLON® commercially available from Toyobo Co., LTD.

The HMWPE fibers useful in this invention have an intrinsic viscosity in decalin at 135 ° C from about 5 deciliter / gram (dl / g) to about 35 dl / g. Such high molecular weight polyethylene fibers are commercially available under the trademark SPECTRA® from Honeywell International Inc. The description of USP 4,413,110 is hereby incorporated by reference to the extent that it is not inconsistent therewith. The HMWPE fibers can also be produced by a rolling and drawing process as described in USP 5,702,657 and sold under the trademark TENSYLON® by ITS Industries Inc. The aramid fibers useful in this invention are described in USP 3,671,542 and are commercially available from He Dupont co. under the trademarks of KEVLAR® and NOMEX® of Tejin Twaron BV under the trade names TWARON®, TECHNORA® and TEIJINCONEX®; of JSC Chim Volokno under the name ARMOS; and from Kamensk Volokno JSC under the names RUSAR and SVM. The co-polymeric poly (p-phenyleneterephthalamide) and p-phenylene terephthalamide aramid fibers having moderately high modulus and tenacity values are particularly useful in the present invention. An example of a p-phenylene terephthalamide copolymer aramid useful in the invention is co-poly- (paraphenylene 3,4'-oxydiphenylene terephthalamide). Also in the In practice of this invention, poly (m-phenylene isophthalamide) fibers are useful. The liquid crystal copolyester fibers suitable for the practice of this invention are described, for example, in US Pat. Nos. 3,975,487, 4,118,372 and 4,161,479. The anhydrous means for encapsulating the PBO fibers in the sealing material include, for example, chemical vapor deposition, polymerization and vapor deposition, in situ polymerization in an anhydrous solution followed by drying, anhydrous sealing solution coating, followed by drying, and other means that do not involve contact of the fibers with aqueous media such as solutions or dispersions. The US Pat. Nos. 4,624,867, 5,447,799, and 6,179,922 disclosing means of vapor deposition of polymers on substrates, and USP Publication 2002/0002219 A1 describing means of in situ polymerization of fluoropolymers on porous substrates are incorporated for this reason as reference in the extent that they are incompatible with it. The preferred means for encapsulating the PBO fibers is the coating of the PBO fibers with an anhydrous solution of the sealing material, followed by drying.

The preferred method of the invention is illustrated schematically in Figure 1 for a network of unidirectional fibers. It will be apparent to a person skilled in the art that modifications of the illustrated apparatus would be made to arrange a flat (for example, placed in air) or woven, knitted, braided, randomly oriented netting. The PBO fibers are supplied from a basket 102 and passed through a combination station 104 to form a unidirectional network. The fibrous web is then passed around stationary bars 20 to spread the yarns in thin layers. The fiber network is then transported under a roller immersed in a bath 105 of an anhydrous solution of sealing material to completely coat each and every filament. The concentration of the sealing material in the anhydrous solvent is such that when the solvent is dried, the sealing material does not completely fill the volume between the filaments. The concentration of the sealing solution is selected in relation to the water vapor permeability of the sealant. The lower the water vapor permeability of the sealant, the lower the concentration of the sealing solution. When working with a network of non-woven fibers such as fibers aligned unidirectionally, the The concentration of the sealant is also subject to the restriction that it must be sufficient to adhere the fibers together in a coherent sheet for structural integrity. Preferably the concentration of the sealing material in the coating solution is from 1% to 25% by weight of the solution (1 to 25% by weight), more preferably from 5 to 20% by weight. A squeegee roller 106 at the outlet of the bath removes excess sealing solution from the fiber network. The coated fiber network is coupled with a carrier network 107 which can be a paper, a plastic film or a fabric. The network of coated fibers is then passed through a furnace 112 heated to evaporate the solvent in the sealing solution thereby encapsulating the fibers in the sealing material. The sealing material partially fills the volume between the fibers and adheres the fibers together to form a coherent sheet. A rolling roller is used to pull the carrier network and the sheet is fibers through the system. The substrate and the fiber sheet are wound on a roller 118 in preparation for the subsequent construction of a laminate or a compound of the invention. The carrier network can be stripped of the fiber sheet or it can become part of the laminate or the final composite.

The sealing material serves as a moisture barrier to protect the PBO fibers and can also serve as an adhesive to provide coherence to a sheet of non-woven fibers. The sealing material has a water vapor permeability of less than 2.5X10"11 cm3 (stp) • cm / (cm2 • sec • Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C, more preferably less than 5X10"11 cm3 (stp) • cm / (cm2 • sec- Pa). The abbreviation "stp" in the permeability units has the commonly understood meaning of "standard temperature and pressure". The type of sealing material is selected in accordance with the end-use requirements for the articles constructed of the sheets of the invention. If a flexible article is necessary, the sealing material is preferably an elastomer with a tensile modulus of less than 6,000 psi (41.4 MPa) when measured by ASTM D638. If a stiff article is needed, stiffness can be obtained either by using a sufficient number of sheets having a low modulus sealing material, or with fewer sheets having a high modulus resinous sealer. When the article is a laminate used in a structural composite, it is preferred that the sealing material have a tensile modulus greater than 1 x 106 psi (6.9 GPa) when measured by ASTM D638. A variety of materials and elastomeric formulations that have a water vapor permeability and a module appropriately low, they can be used as the sealing material of this invention. For example, the following materials are suitable: polyisoprene, natural rubber, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, polychloroprene (Neoprene G), poly (isobutylene-co-isoprene) (natural rubber), block copolymer styrene-isoprene-styrene (brand KRATON® D1107) styrene block copolymer (ethylene-co-butylene) -styrene (brand KRATON® G1650), and polycyclorofluoroethylene. The water vapor permeabilities of some of these elastomers have been reported, for example, in "Polymer Handbook", 2d Ed., J.Brandrup and E.H. Immergut, Editors, Pages III-229 to III-250, John Wiley & Sons, New York 1975 and (1965), and "Fact Sheet K0102 Gas Permeability of KRATOR Polymers", Kraton Polymers, Inc. and are shown in Table I. Table I High modulus sealing resins which may be useful in a laminate of the invention include allyls, amines, cyanates, epoxides, phenolics, unsaturated polyesters, bismaleidyms, rigid polyurethanes, silicones, vinyl esters and their thermoset copolymers and mixtures thereof. Preferred thermosetting vinyl ester resins. Preferably, the vinyl ester in one produced by the esterification of a polyfunctional epoxy resin with an unsaturated monocarboxylic acid, usually methacrylic or acrylic acid. Illustrative vinyl esters include diglycidyl adipate, diglycidyl isophthalate, di- (2,3-epoxybutyl) adipate, (2,3-epoxybutyl) oxalate, di (2,3-epoxyhexyl) succinate, difunctional maleate. (3,4-epoxybutyl), di- (2, 3-epoxyoctyl) pimelate, di (2,3-epoxybutyl) phthalate, di (-2,3-epoxyoctyl) tetrahydrophthalate, di- (4, 5-epoxydecyl), di- (2,3-epoxybutyl) terephthalate, di (2,3-epoxypentoyl) thiodipropionate, di- (5,6-epoxytetradecyl) diphenyldicarboxylate, di- (3,4-) sulfonylbutyrate epoxyheptyl), tri- (2, 3-epoxybutyl) -1,2,4-butanetricarboxylate, (5,6-epoxypentadecyl) maleate, di- (2, 3-epoxybutyl) azelate, di-3,4 citrate -epoxypentadecyl), cyclohexan-1,3-dicarboxylic acid di- (4,5-epoxyoctyl), di (4,5-epoxyoctadecyl) malonate, polyester of bisphenol-A-fumaric acid and similar materials.

Most preferred are epoxy-based vinyl ester resins, such as DERAKANE® resins manufactured by the Dow Chemical Company. The anhydrous solvent is chosen as being a good solvent for the sealing material. An anhydrous solvent in the context of this invention is one that contains less than 0.5% weight of water. Preferably, the anhydrous solvent contains less than 0.1% weight of water. More preferably, the anhydrous solvent contains less than 0.01% weight of water. Solvents for various polymers useful as sealing materials are tabulated for example in "Polymer Handbook", 2nd Ed., J. Brandrup and E.H. Immergut, Editors, Pages IV-241 to IV-262, John Wiley & amp;; Sons, New York 1975, incorporated herein by reference. Preferably the anhydrous solvent has an atmospheric boiling point of less than 150 ° C, more preferably less than 100 ° C, to be easily evaporated. A preferred anhydrous solvent for an elastomeric hydrocarbon sealant is cyclohexane. A preferred anhydrous solvent for vinyl ester resins based on epoxy is methyl ethyl ketone. The invention is also a fibrous sheet composed of PBO fibers in a fiber network, the fibers encapsulated in a sealing material having a water vapor permeability less than 25 X 10"11 cm3 (stp) • cm / (cm2) - sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C and the material of sealing filled between 5 and 99, preferably between 15 and 95 percent of the volume between the fibers. It is also preferred that the sealing material be deposited from an anhydrous solution followed by drying. The sealing material preferably comprises 1 to 50, more preferably 5 to 25, more preferably 5 to 20 weight percent of the fiber sheet. Optionally, a plastic film adheres to one or both sides of the fiber sheet. An article of the invention is a plurality of fibrous sheets of the invention in a stacked arrangement. In a preferred embodiment, the fibers comprising the fibrous sheets are oriented unidirectionally parallel to one another, the direction of the fibers in a given sheet being at an angle to the directions of the fibers in the adjacent sheets. The fibrous sheets may be decoupled or weakly coupled to each other, or adhered together. A preferred article of the invention comprises unidirectional fibrous sheets that fold transversely and adhere to one another. Cross-folding or transverse folding can be done by a continuous transverse stacking operation as described in U.S. Patents 5,173,138 or 5,766,725, incorporated herein by reference to the extent that they are not incompatible therewith, or placed by hand, or by any suitable means.

In a preferred embodiment, the invention comprises a laminate composed of the first and second fibrous sheets of the invention adhered together in a stacked arrangement, wherein the direction of the fibers in the first sheet is at an angle of at least 30 ° with with respect to the direction of the fibers in the second sheet. A preferred article of the invention comprises a plurality of these laminates in a stacked arrangement, not coupled or loosely coupled with one another. In another embodiment, a laminate of the invention comprises one or more fibrous PBO sheets of the invention interspersed with one or more fibrous sheets of high strength fibers of other compositions adhered together in a stacked array, which optionally have a plastic film adhered to one or both sides of the laminate. A preferred form of this embodiment is a laminate comprising in sequence a first, second, third and fourth sheets; said first and fourth leaves that are composed of aramid fibers; said second and third sheets that are composed of PBO fibers, and the sheets comprising the laminate adhere to each other in a stacked array. More preferably, each of the fibrous sheets is composed of unidirectional fibers, with the directions of the fibers in the adjacent sheets which are normal with respect to each other.

Optionally, a plastic film can be adhered to one or both sides of an article of the invention. Preferably, the plastic film is selected from a member selected from the group consisting of polyolefins, polyamides, polyesters, polycarbonates, ionomers, cellulose, cellulose ester, ethyl cellulose, and polyfluorocarbons. The plastic film, if present, preferably comprises from 1 to 40 weight percent of the article. Preferably, the plastic film has a permeance greater than or equal to 5 x 10"9 cm3 (stp) / (cm-sec-Pa), more preferably greater than or equal to 50 x 10" 9 cm3 (stp) / (cm-sec. -Pa), when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C. Since the permeance is equal to the permeability divided by the thickness of the film, the thinner films should be used with the materials of lower permeability and vice versa. For example, for a 0.914 density polyethylene film having a permeability of 0.675 x 10"11 cm3 (stp) -cm / (cm2 • sec- Pa), a film thickness less than or equal to 0.0005 inch is preferred. (0.0014 cm) thick. More preferably, the plastic film is a porous film. The adhesion of the unidirectional PBO fiber sheets of the invention to form the laminates of the invention is preferably done by the application of heat and pressure. Temperatures are used from approximately 90 ° to about | 60 ° C and "pressures from about 100 psi to about 2500 psi (69-17,000 kPa) depending on the type of sealant and the plastic film present In another embodiment, the invention is an article comprising a plurality of the laminates of the invention described above in a stacked arrangement, wherein the laminates are uncoupled or weakly coupled to each other, that is, coupled only at their edges or corners, it will be understood that the number of laminates comprising the article and its dimensions will be determined by the nature of the application Preferably, the article is resistant to penetration and / or ballistically resistant Preferably, a penetration resistant article of the invention meets at least the requirements of NIJ standard 0115.00 for protection against stabbing Type 1. Preferably, a ballistically resistant article of the invention satisfies at least s the requirements of Standard 0101.04 Revision A of the NIJ for Type A body armor. More preferably, a ballistically resistant article of the invention has a specific energy absorption of at least 300 J-m2 / Kg and a V50 rating of at least 1300 ft / sec (396 m / sec) when impacted by a Geco 9 mm bullet, 124 FMJ beads (steel cover). The classification is that speed at which a projectile has a 505 probability of penetrating the article. Even more preferably, an article with ballistic resistance of the invention retains at least 87% of its initial V50 after accelerated aging for four weeks at 70 ° C, 80% relative humidity. More preferably, an article with ballistic resistance of the invention retains at least 85% of its initial V50 classification after accelerated aging for six weeks at 70 ° C, 80% relative humidity. In another embodiment, the invention is a composite comprising a plurality of the unidirectional fiber sheets of the invention adhered together in a stacked array, wherein the direction of the fibers in a given sheet is at an angle relative to the directions of the fibers. the fibers in the adjacent sheets. The following examples are presented to provide a more complete understanding of the invention. The techniques, conditions, materials, proportions and the specific reported data established to illustrate the principles of the invention are exemplary and should not be considered as limiting the scope of the invention. EXAMPLES Comparative Example 1 A PBO unidirectional fiber sheet was prepared using the apparatus shown schematically in FIGURE 1. Various rolls of 1005 denier PBO fibers (trademark ZYLON® AS from Toyobo Co., LTD) were supplied from a basket 102 and passed to through a combination station 104 to form a unidirectional network. The fiber network was passed over and under stationary rods 20 to spread the yarns in thin layers. The fiber network was then carried under a roller immersed in an aqueous suspension bath of an elastomeric styrene-isoprene-styrene block copolymer sealer, to completely coat each filament. The aqueous dispersion, designated PRINLIN®7137AL supplied by Sovereign Specialty Chemicals, Buffalo, NY, is described by the manufacturers as a "resin-modified water-based dispersion, from Kraton® D1107" containing 41 to 45% by weight solids. The network of coated fibers was passed through a squeegee roller 106 at the outlet of the bath, to eliminate the excess sealing dispersion. The coated fiber network was placed in a 0.35 mil (0.00089 cm) polyethylene film carrier web 107 and passed through a heated furnace to evaporate the water and form a coherent fiber sheet containing 20% by weight. weight of sealant of the fibers plus the sealant. The density of fiber area, the sealant and the plastic film was 48.5 g / cm2. the density of the fiber area was 36 g / m2. The area density of the sealant in the fiber sheet was 9 g / m2. The carrier network and the fiber sheet were then wound onto a roller 118 in preparation for the construction of the laminates. Two rollers of the sheet material described above were placed in the cross stacking machine described in USP 5, 173.138. the sheet materials were folded crosswise, 0 ° / 90 °, PBO to PBO, and consolidated at a temperature of 115 ° C and under a pressure of 500 psi (3.5 MPa) to create a laminate with two identical sheets of PBO fibers and polyethylene films on both sides. The laminate was cut into several fragments having side dimensions of 40 cm x 40 cm. Twenty-two were stacked together and sewn around their perimeters to form a number of items for ballistic evaluation. A set of articles was maintained at normal atmospheric conditions. Other articles were subjected to accelerated aging at 70 ° C, 80% relative humidity for four weeks and for 6 weeks. All items were returned to normal atmospheric conditions for a minimum of three days before the ballistic evaluation. The results of the ballistic evaluation with Geco 9 mm bullets, 124 FMJ grains (steel casing) are shown in Table II below. Example 1 A unidirectional fiber sheet was prepared as described in Comparative Example 1 except that instead of aqueous dispersion, the sealant bath was a 20% weight solution of styrene-isoprene-styrene block copolymer elastomer (KRATON ® D1107 by Kraton Polymers, Inc.) in anhydrous cyclohexane containing less than 0.1% by weight of water. The sealing material had a water vapor permeability of 21.5 x 10"11 cm3 (stp) • cm / (cm2 • sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C and a initial traction module of 200 psi (1.4 MPa) when measured by ASTM D638 The coated fiber network was placed in a network 107 carrying polyethylene film and passed through a heated oven to evaporate the cyclohexane and form a coherent fiber sheet wherein each filament was encapsulated in the sealant, the volume between the fibers was partially filled with the sealant The coherent PBO fiber sheet of the invention contained 20% sealant by weight of the sealant plus the fibers. The plastic film carrier and the fiber sheet of the invention were wound onto a roller 118 in preparation for the laminate construction of the invention.

The fraction of the volume between the fibers filled by the sealant was determined as follows. The total area density of the fibers, the sealant and the plastic film was 48.5 g / m2. The area density of the fibers was 36 g / m2. The area density of the sealant in the fiber sheet was 9 g / m2. The PBO fibers had a density of 1.54 g / cm3. The volume actually occupied by the PBO fibers in one square meter of the coated fiber sheet was therefore equal to 36 g / l.54 g / cm 3 = 23.4 cm 3. The sealant, KRATON® D1107 had a density of 0.92 g / cm3. The volume of sealant in one square meter of the coated fiber sheet was therefore equal to 9 g / 0.92 g / cm 3 = 9.8 cm 3. The total thickness of the fiber sheet plus the plastic film was measured to be 0.0043 cm. The thickness of the coated fiber sheet (the fibers plus the sealant) was the total thickness minus the thickness of the plastic film, equal to 0.0043 cm - 0.00089 cm = 0.00341 cm. The volume of one square meter of coated fiber sheet was therefore 0.00341 cm x 104 cm2 = 34.1 cm3. The difference between the volume of the coated fiber sheet and the volume of the fibers was the volume between the fibers = 34.1 cm3 - 23.4 cm3 = 10.7 cm3. The volume of the sealant was 9.8 cm3. Therefore, the sealant occupied 9.8 / 10.7 x 100 = 92% of the volume between the fibers in the coherent PBO fiber sheet of the invention.

Two rolls of the inventive sheet material described above were placed in the cross-folding machine described in US Pat. No. 5,173,138. The sheet materials were folded crosswise, 0 ° / 90 °, PBO to PBO, and consolidated at a temperature of 115 ° C under a pressure of 500 psi (3.5 MPa) to create a laminate with two sheets of fiber PBO identifies and polyethylene films on both sides. The polyethylene films had a water vapor permeance of 7.5 x 10"9 cm3 (stp) / (cm-sec-Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C. cut into several fragments having side dimensions of 40 cm x 40 cm Several of the articles of the invention, each consisting of twenty-two laminates, were formed by stacking and sewing them together around their perimeters.A set of items was evaluated to provide Initial ballistic properties Other articles were subjected to accelerated aging at 70 ° C, 80% relative humidity for 4 weeks and for 6 weeks All articles were returned to normal atmospheric conditions for a minimum of three days before the ballistic evaluation The results of the ballistic evaluation with Geco 9 mm, 124 gr. FMJ (steel deck) bullets are shown in Table II below.

Table II It will be noted that the articles of the invention, where the sealant of the solution was applied in an anhydrous solvent, compared to the articles where sealant of the aqueous dispersion was not applied, showed a significantly higher retention of the ballistic properties after the exposure. at high humidity. The articles of the invention retain more than 87% of their initial V50 classification after four weeks at 70 ° C, 80% R.H. and more than 85% after six weeks. The "breathability" of the articles was provided by incompletely filling the volume between the fibers and providing films with sufficient permeable surface. The articles of the invention exhibit a specific energy absorption against Geco 9mm bullets, 124 gr. FMJ (steel cover) greater than 300 J-m2 / Kg. The articles of the invention meets at least the requirements of Revision A of NIJ Standard 0101.04 for Type IIA body armor. Example 2 A compound of the invention was formed from twenty-two of the laminates described in Example 1 consisting of two sheets of cross-folded PBO fibers and polyethylene films on both surfaces. The laminates are adhered together by molding under a temperature of 115 ° C and a pressure of 1000 psi (6.9 MPa). The compound is believed to meet the requirements of NIJ Standard 0101.04 Revision A for Type IIA body armor, the requirements of NIJ Standard 0115.00 for type 1 stab protection, and retain more than 87% of its V50 rating. initial after four weeks at 70 ° C, 80% RH Example 3 A PBO unidirectional fiber sheet is prepared as described in Example 1 except that the sealant bath is a 10% by weight solution of poly elastomer (isobutylene) (VISTANEX® PIB MM 1-100 from ExxonMobil Chemical Co.) in anhydrous cyclohexane containing less than 0.1% weight of water. The sealing material has a water permeability of 0.28 X 10"11 cm3 (stp) • c / (cm2 • sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C and an initial tensile modulus of less than 6,000 psi (41.3 MPa) when measured by ASTM D638. The coated fiber network is placed in a porous film carrier network of polytetrafluoroethylene having a permeance greater than 50 x 10"9 cm3 (stp) / (cm-sec-Pa) when measured by ASTM E 96-96 ( Procedure E) at 37.8 ° C. The network of coated fibers and the carrier film is passed through a heated furnace to evaporate the cyclohexane and form a coherent fiber sheet where each filament is encapsulated in the sealant. The sealant occupies 51% of the volume between the fibers.The plastic film carrier network and the fiber sheet of the invention are then wound onto a roller 118 in preparation for the construction of the laminates of the invention Two rolls of the inventive sheet material described above are placed in the cross-folding machine described in USP 5,173,138. The sheet materials are folded crosswise, 0 ° / 90 °, PBO a PBO, and they are consolidated at a temperature of 115 ° C under a pressure of 500 psi (3.5 MPa) to create a laminate with two sheets of identical PBO fibers and porous plastic films on both surfaces.

The laminate was cut into several fragments having side dimensions of 40 cm x 40 cm. A number of articles of the invention were formed, each consisting of twenty-two such laminates, stacking and stitching them together around their perimeters. It is believed that the articles of the invention thus formed satisfy at least the requirements of the Revision A of NIJ Standard 0101.04 for Type IIA body armoring and retaining at least 87% of its initial V50 rating after exposure at 70 ° C, 80% relative humidity for 4 weeks. Example 4 A sheet of unidirectional PBO fibers is prepared as described in Example 1, except that the carrier polyethylene film is a porous film. Two rolls of the inventive sheet material are placed in the cross-folding machine described in USP 5,173,138.

The sheet materials are folded transversely, 0 ° / 90 °, PBO to PBO, and they are consolidated at a temperature of 115 ° C and under a pressure of 500 psi (3.5 MPa) to create a laminate with two sheets of identical PBO fibers and porous polyethylene films in both faces Polyethylene films have a water vapor permeance greater than 75 x 10"9 cm3 (stp) / (cm-sec-Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C.

Twenty-two laminates are adhered together by molding under a temperature of 115 ° C and a pressure of 1000 psi (6.9 MPa) to form a compound of the invention. The compound is believed to meet the requirements of revision A of NIJ Standard 0101.04 for Type IIA body armor, requirements of NIJ standard 0115.00 for type 1 stabbing protection, and retains more than 87% of your initial V50 rating for four weeks at 70 ° C, 80% RH Example 5 A woven PBO fabric is 8 mils (0.02 cm) thick and has an area density of 136 g / m2 (Hexcel-Schwebel style 530 fabric consisting of 500 denier ZYLON® AS 500 fibers from Toyobo Co., LTD.) Is passed under a roller immersed in a bath containing an 8% n weight solution of styrene-isoprene-styrene block copolymer elastomer (KRATON® D1107 from Kraton Polymers, Inc.) in anhydrous cyclohexane. containing less than 0.1% by weight of water. Each filament of the fabric is completely coated with the solution. The cloth is passed through a colander roller to remove the excess solution, placed in a carrier network of 0.35 mil polyethylene film (0.00089 cm) and passed through a heated oven to evaporate the solvent. The carrier network and the web The coating of the invention is then rolled onto a roll in preparation for the construction of ballistic resistance articles as described herein below and in the following Example 6. The total area density of the fibers and the sealant is 143 g / m2. The density of area in the dry cloth is 7 g / m2. The volume fraction between the filled fibers by the sealant is determined as follows: The volume occupied by one square meter of uncoated cloth is 100 cm x 100 cm x 0.02 cm = 200 cm3. The volume actually occupied by the fibers in one square meter of uncoated cloth is 136 g / l.54 g / cm3 = 88.3 cm3. The volume between the fibers is therefore 200 cm3 - 88.3 cm3 = 111.7 cm3. The volume occupied by the seal is 7 g / 0.92 g / cm3 = 7.6 cm3. Therefore, the sealant occupies 7.61 cm3 / lll.7 cm3 x 100 = 6.8% of the volume between the fibers. The articles for the ballistic evaluation are formed of twenty-two fragments of the fabric coated with polyethylene film on a surface, which has dimensions of 40 cm x 40 cm stacked together and sewn together around its perimeters. One such article is maintained at normal atmospheric conditions. Another such article is subjected to accelerated aging at 70 ° C, 80% relative humidity for 4 weeks and for 6 weeks. All items are returned to normal atmospheric conditions for a minimum of three days before the ballistic evaluation. It is believed that the articles of the invention meet the requirements of Revision A of NIJ Standard 0101.04 for Type IIA body armor, the requirements of NIJ Standard 0115.00 for protection against type 1 stabbing, and retain more than 87% of your initial V50 score after four weeks at 70 ° C, 80 RH Example 6 The polyethylene film carrier network is stripped of the PBO fabric of the invention, prepared in Example 5 above. Eleven fragments having dimensions of 40 cm x 40 cm are cut from this cloth and each fragment is interposed face to face against two fragments of aramid cloth (Hexel-Schwebel style 705 consisting of fibers of KEVLAR® KM-2 of 850 denier in a flat fabric of 31 x 31 per inch) that has the same dimensions. Each of the sandwiches thus formed is compression molded at a temperature of 115 ° C and under a pressure of 500 psi (3.5 MPa) to create the laminates of the invention. The eleven laminates are stacked together and sewn around their perimeters to form another article of the invention. It is believed that this article of the invention satisfies the requirements of Revision A of NIJ Standard 0101.04. for Type IIA body armor, the NIJ Standard 0115.00 requirements for type 1 stab protection, and retains more than 87% of its initial V50 rating after four weeks at 70 ° C, 80% R.H. Example 7 PBO fibers (ZYLON® AS) cut into lengths of 51 mm were obtained from Toyobo Co. LTD. The chopped fibers were formed on a non-woven sheet (fiber mattress) oriented randomly by a process of placement in air. The fiber mattress is passed through a needle loom to mechanically orient the fibers in the vertical direction and to entangle the fiber mass in a coherent filled fabric. The PBO pledged fabric is passed under a roller immersed in a bath containing a 10% by weight solution of poly (isobutylene) elastomer (VISTANEX® PIB MM 1-100 from ExxonMobil Chemical Co.) in anhydrous cyclohexane containing less than 0.1 % by weight of water. The sealing material has a water vapor permeability of 0.28 x 10"11 cm3 (stp) -cm / (cm2-sec-Pa) when measured by the ASTM E96-95 Standard Test Method (Procedure E) at 37.8 ° C and an initial tensile modulus less than 6,000 psi (41.3 MPa) when measured by ASTM D638.

Each filament of the filled fabric is completely coated with the solution. The fabric is passed through a colander roller to remove the excess solution, placed in a carrier network of 0.35 mil polyethylene film (0.00089 cm) and passed through a heated oven to evaporate the solvent. The sealant occupies 10% of the volume between the fibers. A 1 mil (0.0025 cm) porous polyethylene film is applied to the upper surface of the pledged fabric and the assembly is passed between heated rollers at a temperature of 115 ° C and under a pressure of 500 psi (3.5 MPa) to create a fibrous sheet of the invention. The articles for ballistic evaluation are formed of twenty-four fragments of pleated cloth coated with polyethylene films on both surfaces having dimensions of 40 cm x 40 cm stacked together and sewn around their perimeters. One such article is maintained at normal atmospheric conditions. Another such article is subjected to accelerated aging at 70 ° C, 80% relative humidity for 4 weeks and for 6 weeks. All items are returned to normal atmospheric conditions for a minimum of three days before the ballistic evaluation. It is believed that the articles of the invention meet the requirements of Revision A of NIJ Standard 0101.04 for Type IIA body armor, the NIJ Standard 0115.00 requirements for Type 1 stab protection, and retain more than 87% of their initial V50 rating after four weeks at 70 ° C, 80% R.H. Having thus described the invention in quite full detail, it will be understood that such detail need not be strictly attached but to those other changes and modifications which may be suggested by themselves to a pe skilled in the art, all of which fall within the scope of the invention as defined by the appended claims.

Claims (47)

1. CLAIMS 1. A method for forming a sheet, composed of PBO fibers and resistant to the effects of heat and moisture, characterized in that it comprises the steps of: a) forming a fibrous sheet comprising a plurality of PBO fibers in a fiber network; b) encapsulate the PBO fibers in a sealing material by anhydrous media, the sealing material having a water vapor permeability of less than 25 x 10"11 cm3 (stp) -cm / (cm2-sec-Pa) when is measured by ASTM E 96-95 (Method E) at 37.8 ° C, c) partially fill the volume between the fibers with the sealing material, and d) optionally adhere a plastic film to at least one face of the fibrous sheet. The method of claim 1, characterized in that the PBO fibers comprise from 10 to 100 weight percent of the fiber content of the sheet 3. The method of claim 1, characterized in that the fiber network is selected of the group consisting of a nonwoven, woven, knitted, braided, woven, flat nonwoven oriented randomly, and a non-woven oriented unidirectionally. 4. The method of claim 1, characterized in that the fibers in the network are aligned unidirectionally such that they are substantially parallel to one another. The method of claim 1, characterized in that said sealing material fills from 5% to 99% of the volume between the fibers. The method of claim 1, characterized in that said sealing material fills from 15% to 95% of the volume between the fibers. The method of claim 1, characterized in that said sealing material has a water vapor permeability of less than 5 x 10"11 cm3 (stp) • cm / (cm2 - sec • Pa) when measured by ASTM E 96-95 (Method E) at 37.8 ° C. 8. The method of claim 1, characterized in that the anhydrous medium for encapsulating the fibers is selected from the group consisting of chemical vapor deposition, vapor phase polymerization, an anhydrous solution followed by drying, and coating by an anhydrous sealing solution followed by drying 9. The method of claim 1, characterized in that the anhydrous medium for encapsulating the fibers is coated by an anhydrous sealant solution followed by drying. 10. The method of claim 9, characterized in that the solvent in said anhydrous sealant solution has an atmospheric boiling point of less than 150 ° C. The method of claim 9, characterized in that the solvent in said anhydrous sealant solution has an atmospheric boiling point of less than 100 ° C. 12. A method for forming a ballistically resistant article comprising PBO fibers that have at least 87% of their initial V50 rating after conditioning for four weeks at 70 ° C, 80% relative humidity, characterized in that it comprises the steps of: a) forming a fibrous sheet comprising a plurality of PBO fibers in a fiber network; b) encapsulate the PBO fibers in a sealing material by anhydrous means, the sealing material having a water vapor permeability of less than 25 x 10"11 cm3 (stp) -cm / (cm2-sec- Pa) when is measured by ASTM E 96-95 (Procedure E) at 37.8 ° C. c) partially fill the volume between the fibers with the sealing material, d) optionally adhere a plastic film to at least one face of the fibrous sheet; ) stacking a plurality of the fibrous sheets on one another in a decoupled or weakly coupled arrangement. 13. A method for forming a ballistically resistant article comprising PBO fibers and retaining at least 87% of its initial V50 rating after conditioning for four weeks at 70 ° C, 80% relative humidity, characterized in that it comprises the steps of: a) aligning a plurality of PBO fibers in a unidirectional flat sheet b), encapsulating the PBO fibers in a sealing material by anhydrous means, the sealing material having a water vapor permeability of less than 25 x 10" cm3 (stp) • cm / (cm2 • sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C and which partially fills the volume between the fibers; c) adhering the fibers to form a coherent sheet; d) stacking a first and a second coherent sheets one on top of the other, the direction of the fibers in the first sheet that is at an angle of at least 30 ° with respect to the direction of the fibers in the second sheet; e) adhering the first and second coherent sheets to form a laminate; f) optionally adhering a plastic film to one or both sides of the laminate; and g) stacking a plurality of laminates one or the other in a decoupled or weakly coupled arrangement. 14. The fibrous sheet composed of PBO fibers in a network of fibers, said fibers that are encapsulated in a sealing material having a water vapor permeability of less than 25 x 10"11 cm3 (stp) • cm / (cm2 • sec - Pa) when measured by ASTM E 96-95 (Method E) at 37.8 ° C, characterized in that said sealing material fills between 5 and 99 percent of the volume between the fibers, and optionally has a plastic film adhered to one or both sides of the sheet 15. The fibrous sheet of claim 14, characterized in that the fiber network is selected from the group consisting of a woven, knitted, woven, braided, woven, flat nonwoven fabric oriented in a random manner, and a non-woven oriented unidirectionally 16. The fibrous sheet of claim 14, characterized in that the fibers in the network are aligned unidirectionally such that they are substantially parallel to each other 17. The fibrous sheet of claim 14 , expensive cterized because said sealing material fills from 15% to 95% of the volume between the fibers. 18. The fibrous sheet of claim 14, characterized in that the PBO fibers are poly (2-phenylene-2,6-benzobisoxazole). 19. The fibrous sheet of claim 14, characterized in that the PBO fibers comprise from 10 to 100% by weight of the fiber content of said article. 20. The fibrous sheet of claim 14, characterized in that said sealing material comprises from 1 to 50 weight percent of the article. 21. The fibrous sheet of claim 14, characterized in that said sealing material comprises from 5 to 25 weight percent of the article. 22. The fibrous sheet of claim 14, characterized in that said sealing material comprises from 5 to 20 weight percent of the article. 23. The fibrous sheet of claim 14, characterized in that said sealing material has a vapor permeability of less than 5 x 10"11 cm3 (stp) • cm / (cm2 - sec- Pa) when measured by ASTM. E 96-95 (Method E) at 37.8 ° C. 24. The fibrous sheet of claim 14, characterized in that said sealing material is an elastomeric material having a tensile modulus of less than 6,000 psi (41.3 MPa) when measured by ASTM D638 25. The fibrous sheet of claim 14, characterized in that the plastic film is a member selected from the group consisting of polyolefins, polyamides, polyesters, polycarbonates, ionomers, cellulose, cellulose ester, ethyl cellulose, and polyfluorocarbons. 26. The fibrous sheet of claim 14, characterized in that the plastic film has a water vapor permeance greater than or equal to 5 x 10"9 cm3 (stp) / (cm-sec-Pa) when measured by ASTM E 96-95 (Method E) at 37.8 ° C. 27. The fibrous sheet of claim 14, characterized in that the plastic film has a water vapor permeance greater than or equal to 5 x 10"9 cm3 (stp) / ( cm-sec-Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C. 28. The fibrous sheet of claim 14, characterized in that the plastic film is porous. 29. The fibrous sheet of claim 14, characterized in that the plastic film comprises from 1 to 40 weight percent of the sheet. 30. An article comprising a plurality of fibrous sheets of claim 14, in a stacked arrangement, characterized in that the fibrous sheets are decoupled or weakly or loosely coupled with one another. 31. The article of claim 30, characterized in that, it satisfies at least the requirements of Revision A of Standard 0101.04 of the NIJ for bundle body armor. 32. The article of claim 30, characterized in that it has a specific energy absorption of at least 300 J-m2 (Kg and a V50 rating of at least 1300 ft / sec (396 m / sec) when hit by a bullet 9 mm Geco, 124 beads, FMJ (steel cover) 33. A laminate, characterized in that it comprises one or more fibrous sheets of claim 14, interspersed with one or more fibrous sheets of high strength fibers of other compositions adhered together in a stacked arrangement, and optionally having a plastic film adhered to one or both sides of the laminate 34. The laminate of claim 30, comprising in sequence, a first, second, third, and fourth sheets.; characterized in that said first and fourth sheets are composed of aramid fibers and said second and third sheets are composed of the fibrous sheets of claim 14. 35. The laminate of claim 34, characterized in that said first and fourth sheets are composed of unidirectional aramid fibers, the directions of the fibers in said first and fourth sheets that are normal with each other; said second and third sheets are composed of the fibrous sheets of claim 22, the directions of the fibers in said second and third sheets that are normal with each other; the direction of the fibers in said first sheet which are normal to the directions of the fibers in said second sheet, the direction of the fibers in said third sheet which is normal to the direction of the fibers in said fourth sheet. 36. A laminate, comprising a plurality of the unidirectional fibrous sheets of claim 22 adhered together in a stacked arrangement, characterized in that, the direction of the fibers in a given sheet is at an angle with respect to the direction of the fibers in the adjacent sheets, optionally having a plastic film adhered to one or both sides of the laminate. 37. The laminate of claim 34, characterized in that the sealing material has an initial tensile modulus equal to or greater than 1 x 106 psi (6.9 GPa) when measured by ASTM D638. 38. The laminate of claim 34, characterized in that, a first and a second unidirectional fibrous sheets of claim 22, adhere together in a stacked arrangement, the direction of the fibers in said first sheet that is at an angle of at least 30 ° in relation to the direction of the fibers in said second sheet. 39. An article comprising a plurality of laminates of claim 34 in a stacked arrangement, characterized in that the laminates are decoupled or coupled weakly or loosely with one another. 40. The article of claim 39, characterized in that it satisfies at least the requirements of Revision A of NIJ Standard 0101.04 for body wrapping of the bundle type. 41. The article of claim 39, characterized in that it has a specific energy absorption of at least 300 J-m2 / Kg and a V50 rating of at least 1300 ft / sec (396 m / sec) when hit by a 9 mm Geco ball, 124 grains, FMJ (steel casing). 42. The article of claim 39, characterized in that it has a retention of 87% or more of its initial V50 classification after accelerated aging for four weeks at 70 ° C, 80% relative humidity. 43. The article of claim 39, characterized in that it has a retention of 85% or greater of its initial V50 rating after accelerated aging for six weeks at 70 ° C, 80% relative humidity. 44. The article of claim 39, characterized in that, it satisfies at least the requirements of the Standard 0115. 00 of the NIJ for protection against stabbing Type 1. 45. The fibrous sheet of claim 14, characterized in that the fibers have been encapsulated by an anhydrous process selected from the group consisting of chemical vapor deposition, vapor phase polymerization. , polymerization in an anhydrous solution followed by drying, and coating by a sealant solution followed by drying. 46. The fibrous sheet of claim 14, characterized in that the fibers have been encapsulated by coating with a sealant solution followed by drying. 47. PBO fibers encapsulated in a sealing material having a water vapor permeability of less than 25 x 10"11 cm3 (stp) • cm / (cm2 • sec- Pa) when measured by ASTM E 96-95 (Procedure E) at 37.8 ° C.