MX2008010521A - Method of making improved ballistic products - Google Patents

Abstract

A method of making a ballistic resistant composite material having improved resistance to high energy rifle bullets and the like. The method comprises providing at least one fibrous layer comprising a network of high tenacity aramid fibers. The fibrous layer is coated with a thermoplastic polyurethane resin. The coated fibrous layer is molded at a pressure of at least about 1,500 psi (10.3 MPa). Preferably, a plurality of fibrous layers are employed, each of which is formed from unidirectionally oriented aramid fibers in a thermoplastic polyurethane resin matrix. Adjacent fibrous layers are preferably oriented at 90°with respect to each other.

Description

METHOD FOR MANUFACTURING IMPROVED BALLISTIC IMPACT RESISTANT PRODUCTS BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to products resistant to ballistic impacts, in particular products resistant to ballistic impacts formed from aramid fiber material. DESCRIPTION OF THE RELATED ART Products resistant to ballistic impacts for vests and the like are known in the art. Many of these products are based on high tenacity fibers such as aramid fibers. Even though these products have excellent properties and have achieved commercial success, there is a constant need to improve the properties of armor products, such as shield products to protect the body. In particular, it would be desirable to provide products resistant to ballistic impacts that have improved resistance to bullets of high-energy rifles and the like. SUMMARY OF THE INVENTION In accordance with this invention, there is provided a method for manufacturing a ballistic impact resistant composite having improved resistance to bullets of high energy rifles and the like, the method comprising providing at least one layer fibrous that comprises a network of high tenacity aramid fibers; coating the fibrous layer with a thermoplastic polyurethane resin; and molding the fibrous layer at a pressure of at least about 10.3 Pa (1,500 psi). The invention also provides a method for manufacturing a ballistic impact resistant composite having improved resistance to high energy rifle bullets and the like, the method comprising supplying a first fibrous layer comprising a network of high aramid fibers. tenacity; coating the first fibrous layer with a thermoplastic polyurethane resin; providing a second fibrous layer comprising a network of high tenacity aramid fibers; coating the second fibrous layer with a thermoplastic polyurethane resin; and molding the first fibrous layer and the second fibrous layer at a pressure of at least about 10.3 MPa (1,500 psi). In addition, the invention provides a method for manufacturing a ballistic impact resistant composite having improved resistance to high energy rifle bullets and the like, the method comprising supplying a first fibrous nonwoven layer comprising a fiber network. of high tenacity aramid; coating the first fibrous non-woven layer with a thermoplastic polyurethane resin; providing a second fibrous nonwoven layer comprising a network of high tenacity aramid fibers; cover the second fibrous non-woven layer with a thermoplastic polyurethane resin; placing the first nonwoven fibrous layer and the second fibrous nonwoven layer such that the first nonwoven fibrous layer and the second fibrous nonwoven layer are oriented relative to one another; and molding the first fibrous layer and the second fibrous layer at a pressure of at least about 10.3 MPa (1,500 psi). This invention also offers a method for improving the resistance of a body armor resistant to ballistic impacts to rifle bullets. high energy and the like, the method comprises the supply of a first fibrous layer comprising a network of high tenacity aramid fibers; coating the first fibrous layer with a thermoplastic polyurethane resin; supplying a second fibrous layer comprising a network of high tenacity aramid fibers; coating the second fibrous layer with a thermoplastic polyurethane resin; molding the first fibrous layer and the second fibrous layer at a pressure of at least about 10.3 MPa (1, 500 psi) to form a molded article; and forming the armor for the body at least in part from the molded article. It has been surprisingly discovered that when a thermoplastic polyurethane resin is used to form a composite aramid fibrous structure and the composite structure is formed under high pressure, the composite structure has improved ballistic impact resistance to bullets from high-energy rifles and the like. This is especially unexpected since similar results have not been observed with aramid compounds using other known coating resins. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to compounds formed from aramid fibers having improved ballistic impact resistance, especially to high energy rifle bullets. These compounds are especially useful in resistant ballistic armoring articles, both flexible and rigid. Examples include armor for the body, helmets, covers and the like. Bullets from high-energy rifles are bullets in which the energy level is generally from about 1,500 to about 3,500 joules, or more. Examples of such bullets are the bullet 80 (also known as the NATO bullet), Dragnov LPS and the like. For the purposes of the present invention, a fiber is an elongated body whose longitudinal dimension is much greater than the transverse dimensions of width and thickness. Accordingly, the term "fiber" includes monofilament, multifilament, tapes, strips, and other forms of staple or discontinuous fibers and the like having regular or irregular cross sections. The term "fiber" includes a plurality of any of the foregoing or a combination thereof. A thread is a thread that consists of many fibers or filaments. The cross sections of fibers useful in the present invention may vary widely. They can be circular, flat or elongated in cross section. They may also be of irregular or regular multi-lobular cross section having one or more regular or irregular lobes protruding from the linear or longitudinal axis of the filament. It is particularly preferable that the fibers be of substantially circular, flat or elongated cross section, more preferably the fibers are of substantially circular cross section. As used herein, the term "high tenacity fibers" refers to fibers that have a tenacity equal to or greater than about 7 g / d. These fibers preferably have initial tension moduli of at least about 150 g / d and energy to rupture of at least about 8 J / g in accordance with that measured by ASTM D2256. Preferred fibers are those fibers having a tenacity equal to or greater than about 10 g / d, a modulus of tension greater than or equal to about 200 g / d and an energy at break equal to or greater than about 20 J / g. Particularly preferred fibers are those fibers having a tenacity equal to or greater than about 16 g / d, a modulus of tension equal to or greater than approximately 400 g / d, and an energy at rupture equal to or greater than approximately 27 J / g. Among these particularly preferred embodiments, embodiments in which the tenacity of the fibers is equal to or greater than about 22 g / d, the tension modulus is equal to or greater than about 500 g / d, and the energy at the break is equal to or greater than approximately 27 J / g. As used herein, the terms "initial tension modulus", "tension modulus" and "modulus" refer to the modulus of elasticity in accordance with that measured by AST 2256 for a yarn and by ASTM D638 for a matrix material. Aramid fibers are known in the art. Suitable aramid fibers useful in the present invention are formed from aromatic polyamides, such as those described in U.S. Patent No. 3,671,542, the disclosure of which is expressly incorporated herein by reference insofar as it is not inconsistent. Preferred aramid fibers will have a tenacity of at least about 20 g / d, an initial tension modulus of at least about 200 g / d and an energy at break of at least about 8 J / g, and in particular preferred, the aramid fibers will have a toughness of at least about 20 g / d, an initial tension modulus of at least about 400 g / d and an energy at break of at least about 20 J / g. More preferred aramid fibers will have a tenacity of at least about 23 g / d, a modulus of at least about 500 g / d, and a breaking energy of at least about 30 J / g. For example, poly (p-phenylene terephthalamide) filaments having moderately high modulus and tenacity values are particularly useful in the formation of ballistic resistant compounds. Examples are Twaron® T2000 from Teijin having a denier of 1000. Another example is Kevlar® 29 having 500 g / d and 22 g / d and Kevlar® 49 having 1000 g / d and 22 g / d as initial tension modulus values. and tenacity, respectively, both available in du Pont. Copolymers of poly (p-phenylene terephthalamide) can also be used such as co-poly (p-phenylene terephthalamide 3,4 'oxydiphenylene terephthalamide). Poly (m-phenylene isophthalamide) fibers commercially produced by du Pont under the trade name Nomex® are also useful in the practice of the present invention. The fibers can be any suitable denier such as from about 50 to about 3000 denier, more preferably from about 200 to about 3000 denier, preferably even higher from about 650 to about 1500 denier, and most especially from about 800 to about 1300 denier The aramid fibers are formed in at least one layer of fibrous web. Preferably, the fibrous web is a non-woven fabric, even when other types of fabrics can also be used such as for example woven fabrics or knitted fabrics. In the case of woven fabrics, they can be woven with yarns having different fibers in the warp and in the weft, or in other directions. Preferably, there are at least two layers of fibrous webs used to prepare the ballistic resistant composites. A particularly preferred configuration of the fibers is in a network wherein the fibers are aligned unidirectionally such that they are substantially parallel to each other along a common fiber direction. Alternatively, a non-woven fabric can be used where the fibers are formed into felt in a random orientation. Preferably, at least about 50% by weight of the fibers in the non-woven fabric are high tenacity aramid fibers, more preferably at least about 75% by weight of the fibers in the fabric are aramid fibers of the aramid. high tenacity, and most preferably substantially all of the fibers in the fabric are a high tenacity aramid fibers. The threads can be in essentially parallel alignment, or the threads can be crooked, wrapped or tangled Fabrics formed from unidirectionally oriented fibers typically have a fiber layer extending in one direction and a second fiber layer extending in another direction (preferably 90 °) compared to the fibers of the first layer. When the individual folds are unidirectionally oriented fibers, the successive folds are formed rotated relative to each other, for example at angles of 0 ° / 90 °, 0 ° / 90 ° / 0 ° / 90 °, or 0 ° / 45 ° / 90o / 45o / 0 ° or at other angles. It is convenient to characterize the geometries of the compounds of the present invention by the geometries of the fibers. A suitable arrangement of this type is a fibrous layer in which the fibers are aligned parallel to each other along a common fiber direction (known as a "unidirectionally aligned fiber network"). Successive layers of such unidirectionally aligned fibers can be rotated relative to the previous layer. Preferably, the fibrous layers of the composite are folded crosswise, ie, with the fiber direction of the unidirectional fibers of each network layer rotated relative to the fiber direction of the unidirectional fibers of the adjacent layers. An example is a five-layer article with the second layer, third layer, fourth layer, and fifth layer rotated + 45 °, -45 °, 90 ° and 0 ° in relation to the first layer. A preferred example includes two layers with a 0 ° / 90 ° arrangement. Such rotated unidirectional alignments are described, for example, in U.S. Patent Nos. 4,623,574; 4,737,402; 4,748,064; and 4,916,000. In general, the fibrous layers of the present invention are preferably formed by building a network of fibers initially and then coating the network with a matrix composition. As used herein, the term "coat" is used broadly to describe a fibrous network wherein the individual fibers have either a continuous layer of the matrix composition surrounding the fibers or a discontinuous layer of the matrix composition. on the surface of the fibers. In the first case, it can be said that the fibers are fully integrated into the matrix composition. The terms "coating" and "impregnation" are used interchangeably here. Fibrous networks can be constructed through several methods. In the preferred case of non-woven fibrous webs of unidirectionally aligned fibers, groups of high tenacity filament yarns are supplied from a creel and are carried through guides and one or more dispersion rods in a collimation comb before of the coating with the matrix material. The collimation comb aligns the filaments in a coplanar manner and in • substantially unidirectional form. The method of the present invention initially includes the formation of the fiber network layer, preferably a unidirectional network in accordance with that described above, by applying a solution, dispersion or emulsion of the matrix composition in the fiber network layer, and after drying the network layer of matrix coated fibers. The solution, dispersion or emulsion is preferably an aqueous solution of the polyurethane resin that can be sprayed onto the filaments. Alternatively, the filament structure may be coated with the aqueous solution, dispersion or emulsion by immersion or through roller applicator or the like. After coating, the coated fibrous layer can then be passed through a drying oven where the network layer of coated fibers (unicinta (unitape)) is subjected to sufficient heat to evaporate the water in the matrix composition. The coated fibrous web may then be placed in a carrier fabric which may be a paper substrate or a film, or the fibers may be initially placed in a carrier fabric prior to coating with the matrix resin. The substrate and the unicinta can then be rolled up in a continuous roll in a known manner. The unicinta can be cut in discrete and placed sheets in a stack for formation in the compound for final use. As mentioned previously, the most preferred compound is a compound in which the fiber network of each layer is unidirectionally aligned and oriented in such a way that the directions of fibers in successive layers is the 0 ° / 90 ° orientation. In the most preferred embodiment, two fiber network layers are folded transversely in the 0 ° / 90 ° configuration and then consolidated to form a sub-assembly precursor. Two layers of fiber webs can be continuously folded, preferably by cutting one of the networks into stretches that can be placed successively across the width of the other network in an 0 ° / 90 ° orientation. Equipment for continuous cross-folding of the fibrous layers is known, as described for example in U.S. Patent Nos. 5,173,138 and 5,766,725. The resulting continuous two-fold sub-assembly can then be wound on a roll with a layer of separation material between each fold. The individual sheets of the composite can be adhered to each other by contact either under the application of heat and without pressure or with a relatively low pressure. As mentioned above, the high tenacity fibers of each layer are covered with the matrix composition and then the matrix / fiber combination composition is consolidated.

By "consolidation" it is meant that the matrix material and the fibrous layer are combined into a single unitary layer. Consolidation can occur through pull-out, cooling, heating, relatively low pressure or a combination of these measures. In an alternative embodiment, a sub-assembly of four folds is formed wherein the successive layers are oriented in an orientation 0 ° / 90o / 0 ° / 90o. When it is ready to form the compound for final use, the roll is unrolled and the separation material removed. The multiple fold sub-assembly is then cut into discrete sheets, stacked in multiple folds and then molded in order to form the finished shape and cure the matrix resin, as described below. The matrix resin for the fibers in the fibrous layers is a thermoplastic polyurethane resin. The polyurethane resin may be a homopolymer or a copolymer, and mixtures of one or more of these resins may also be employed herein. Such resins are known in the art and are commercially available. Preferably, such resins are provided in an aqueous system for ease of use. These resins are typically available in the form of solutions, dispersions or aqueous emulsions, wherein the solid components may be within a range of about 20 to about 80% by weight, with greater preferably from about 40 to about 60% by weight, with the remaining weight being water. Such resin compositions are disclosed in commonly assigned co-pending US patent serial number 11 / 213,253. Conventional additives such as fillers and the like may be included in the resin composition. The ratio between the resin matrix material and the fiber in the composite layers can vary widely according to the end use. The polyurethane resin, in a solid base, preferably forms from about 1 to about 40 weight percent, more preferably from about 10 to about 30 weight percent, and more preferably from about 15 to about 28 percent in weight of each composite layer. Preferably, the same thermoplastic polyurethane resin is used in at least two of the fibrous layers, and more preferably in all the fibrous layers. The method of this invention includes the formation of such composite materials of this invention which can be formed from individual sheets by consolidation under high pressure. The pressure employed here is at least 10.3 MPa (1, 500 psi), more preferably at least about 13.8 MPa (2000 psi), with even greater preference at least about 17.2 MPa (2,500 psi) and with greater preference for at least approximately 20.7 MPa (3,000 psi). The pressures employed herein are preferably within a range of about 10.3 MPa (1,500 psi) to about 27.6 MPa (4,000 psi). Typical temperatures useful in the method of this invention are, for example, temperatures within a range of about 24 to 160 ° C (75 to 320 ° F), more preferably at temperatures within a range of about 66 to 152 ° C. (150 to 305 ° F) and more preferably temperatures within a range of about 104 to 132 ° C (220 to 270 ° F). The composite structure can be molded in any suitable molding apparatus to form the desired structure. Examples of such equipment include hydraulic presses that provide high pressure molding. In one embodiment, the individual fibrous layers are placed in a molding press and the layers are molded under the above indicated temperature and elevated pressure for a suitable period of time, such as from about 0.5 to about 30 minutes, more preferably about 10 to about 20. The number of layers in the composite material depends on the particular end use. More preferably, each compound is formed of two fibrous layers that are oriented 80 ° with respect to each other and have been consolidated into one structure. As mentioned above, alternatively the compound may be formed of two groups of such individual structures, such that a total of four layers of fibers is employed; in this case, two of the consolidated two-fold structures are consolidated together in a four-fold sub-assembly. The number of layers of compound used in articles formed from there varies according to the final use of the article. For example, there may be at least about 40 layers, preferably at least about 150 layers, and preferably within a range of about 40 to about 400 layers, of the two-fold assemblies that are used to mold the desired product. The molded articles can have any desired shape. For use in vests and the like, preferably the layers are molded in a relatively flat configuration. Similarly, for ballistic panels, the layers are preferably molded in a substantially planar configuration. For other articles, such as helmets and the like, the layers are molded into the desired shape of the final product. The molded articles can be used as hard or flexible shielding as desired, depending on the molding conditions. The molded articles can be combined with other rigid, flexible and / or molded articles to provide a particularly desirable ballistics and other properties. Such articles can be formed of aramid and / or other high tenacity fibers, using the same matrix resin or a matrix resin different from that used here, or from other materials. One or more plastic films may be included in the composite to allow different composite layers to slide over each other to facilitate formation in a body shape and facilitate use. These plastic films can be typically adhered on one or both surfaces of each compound. Any suitable plastic film can be used, such as films made of polyolefins. Examples of such films are linear low density polyethylene (LLDPE) films, ultra high molecular weight polyethylene (UHMWPE) films, polyester films, nylon films, polycarbonate films, and the like. These films can be of any desirable thickness. Typical thicknesses are within a range of about 2.5 to 30 um (0.1 to 1.2 thousandth of an inch), more preferably of about 5 to 25 um (0.2 to 1 thousandth of an inch), and more preferably of about 7.5 to 12.5 um (0.3 to 0.5 thousandth of an inch). More preferably, LLDPE films are used. The films can be formed as part of each sub-assembly, or the films can be introduced between sub-assemblies when placed in the mold. The films may be on one side or both sides of the sub-assemblies and / or final molded product. Several constructions are known for fiber reinforced composites used in impact resistant and ballistic articles. These compounds exhibit various degrees of resistance to penetration by high velocity impact of projectiles such as bullets, shrapnel and fragments, and the like. Examples of such constructions are disclosed, for example, in U.S. Patent Nos. 6,268,301, 6,248,676, 6,219,842; 5,677,029; 5,471,906; 5,196,252; 5,187,023; 5,185,195; 5,175,040; and 5,167,876. In one embodiment of the invention, a vest or other body armor or other article is formed in a conventional manner from several layers of the composite material. These layers are preferably not laminated together, but may be sewn together in order to prevent the sliding of the individual folds relative to each other. For example, the layers may be adhered with glue at each corner. Alternatively, the layers may be wrapped globally in a bag or other coating. The following non-limiting examples are presented in order to provide a more complete understanding of the invention. The techniques, conditions, materials, proportions and specific reported data presented forE. illustrating the principles of the present invention are exemplary and should not be considered as limiting the scope of the invention. All percentages are given by weight, unless otherwise indicated. EXAMPLES Example 1 A non-woven two-ply composite was formed from layers of aramid fiber with a denier of 1000 and a toughness of 26 g / d (Twaron® T2000 from Teijin). Units were prepared by passing the aramid fibers from a creel and through a combing station to form a unidirectional network. The fiber network was then placed in a carrier fabric and the fibers were coated with a matrix resin. The resin was a dispersion of a thermoplastic polyurethane resin, specifically a copolymer mixture of polyurethane resins in water (40-60% resin) described by the manufacturer as having a relative density of 1.05 g / cc at 23 ° C and a viscosity from 40 cps to 23 ° C. The network of coated fibers was then passed through a furnace to evaporate the water in the composition and was rolled on a roll, with the carrier fabric removed therefrom, in preparation for the formation of the composite. The resulting structure contained 16% by weight of the polyurethane resin. Two continuous rolls of materials pre-impregnated unidirectional fibers were prepared in this way. Two unicintas of this type were folded crosswise at 90 ° and consolidated to create a laminate with two sheets of identical aramid fibers. Panels of this material of a size of 30.5 x 30.5 cm (12 x 12 inches) were used to form the composite structure of multiple layers. A total of 270 2-ply construction layers were placed in a die die of a hydraulic press and molded at 115.6 ° C (240 ° F) at a molding pressure of 10.3 MPa (1,500 psi) for a period of 20 minutes. The laminate that was formed had a substantially flat configuration. After molding, the laminate was allowed to cool to room temperature. The ballistic characteristics of multiple layers of the 4-fold composite were determined. The bullet was a NATO bullet (also known as an M80 bullet) whose size was 7.62 x 51 mm. The projectile is a high-energy rifle bullet. The resistance to ballistic impacts was determined in accordance with UN Standard NIJ 0101.04. The results are shown in Table 1 below. The V50 calculation was determined based on the average of 6-10 pairs of bullets detained in the structure and penetrating the structure. The velocity V50 is the speed at which the projectile has a penetration probability of 50%.

Comparative Example 2 Example 1 was repeated except that the molding pressure was 3.4 Pa (500 psi). The samples were again tested for their resistance to ballistic impacts using the same type of bullet and the results are shown in Table 1 below. Example 3 Example 1 was repeated, except that a total of 315 layers of the composite to form the panels. The samples were tested again to determine their resistance to ballistic impacts using the same type of bullets, and the results are shown in Table 1, below. Comparative Example 4 Example 3 was repeated except that the molding pressure was 3.4 MPa (500 psi). The samples were tested again to determine their resistance to ballistic impacts using the same type of bullets, and the results are shown in Table 1, below. Example 5 Example 1 was repeated except that the total of 360 layers of the compound was used to form the panels. The samples were tested again to determine their resistance to ballistic impacts using the same type of bullets, and the results are shown in Table 1, below. Comparative Example 6 Example 5 was repeated, except that the molding pressure was 3.4 MPa (500 psi). The samples were tested again to determine their resistance to ballistic impacts using the same type of bullets, and the results are shown in Table 1, below. Table 1 * = comparative example As can be seen from the data above, when the matrix resin was a polyurethane copolymer and the composite was molded at high pressure (17.2 MPa (2500 psi)) in accordance with Example 1, the strength to ballistic impacts was substantially better than using the same matrix resin but molded at a low pressure in accordance with Comparative Example 1. This result was consistent when the number of layers was increased from 270 to 315 to 360 in accordance with that indicated in the examples. Furthermore, it can be seen that a smaller number of layers of the composite formed in accordance with the present invention can be used to obtain similar ballistic properties than in the case of a larger number of layers that were molded under low pressure. As a result, the weight of the composite molded under high pressures can be reduced without sacrificing ballistic properties. Comparative Examples 7-9 In Example 7, Example 1 was repeated, except that the matrix resin was Kraton® D1107 a thermoplastic elastomer of styrene-isoprene-styrene block copolymer and the resin content of the composite layers was 20% by weight. A total of 250 layers of the 2-fold pre-assembly was used to form the test panels that were molded at 121.1 ° C (250 ° F) for 30 minutes at a molding pressure of 1.4 Pa (200 psi). The samples were tested for their resistance to ballistic impacts using the same type of bullets in accordance with MIL-STD-662-F. The results are shown in Table 2 below. In Example 8, Example 7 was repeated, except that the molding pressure was 13.8 MPa (2,000 psi). The samples they were tested for ballistic performance using the same type of bullets, and the results are shown in Table 2, below. In Example 9, Example 7 was repeated, except that the molding pressure was 27.6 MPa (4,000 psi). Samples were tested for their ballistic performance using the same type of bullets and the results are shown in Table 2, below. Table 2 * = comparative example From Table 2, it can be seen that as the molding pressure is raised using a compound having a styrene-isoprene-styrene thermoplastic elastomeric resin, the ballistic properties were not substantially improved. Consequently, the substantial improvement of observed ballistic properties with compounds that are formed under high pressure and that use The polyurethane matrix is not found in compounds that use a thermoplastic elastomer matrix resin. Comparative Examples 10 and 11 In Example 10, Example 7 was repeated, except that the matrix resin was an epoxy vinyl ester resin (Derkane 411). The resin content of the composite layers was also 20% by weight. A total of 250 layers of the 2-fold pre-assembly was used to form the test panels. They were molded at 93.3 ° C (200 ° F) for 30 minutes at a molding pressure of 1.4 MPa (200 psi). The samples were tested for their resistance to ballistic impacts using the same type of bullets and the results are shown in Table 3, below. In Example 11, Example 10 was repeated, except that the molding pressure was 6.1 MPa (889 psi). The samples were tested for ballistic performance using the same type of bullets, and the results are shown in Table 3, below. Table 3 * = comparative example Comparative Examples 10 and 11, Table 3 also illustrate that substantial improvements in ballistic properties are not obtained when the molding pressure is increased in compounds using another conventional matrix resin (epoxy vinyl ester). Comparative Examples 12 and 13 In Example 12, Example 10 was repeated, except that the total number of layers was 36. Samples were tested for ballistic performance using a 9mm gunshot with a metal jacket complete The molding pressure was again 1.4 MPa (200 psi). The ballistic results are shown in Table 4, down. In Example 13, Example 12 was repeated, except that the molding pressure was 6.1 MPa (889 psi). The samples were tested for ballistic performance using a 9mm pistol bullet with a full metal jacket, and the results are shown in Table 4, below. Table 4 * = Comparative Example Comparative Examples 12 and 13 similarly show that substantial improvements in ballistic properties are not obtained when the molding pressure is increased in compounds using another conventional matrix resin (epoxy vinylester) where the number of layers is reduced. The ballistic improvement is not observed with greater pressures with a pistol bullet. Example 14 The aramid ballistic materials of this invention were tested to determine their structural properties. Panels of the same size were formed as in Example 1 under similar conditions, except that the molding pressure was 10.3 MPa (1, 500 psi). A total of 45 layers were molded and samples measuring 2.5 cm (1 inch) by 15.24 cm (6 inches) were cut from the panels. The structural properties were determined in accordance with ASTM D790, and the results are shown in Table 5, below. Comparative Example 15 Example 14 was repeated, except that the molding pressure was 1.0 MPa (150 psi). The structural properties were determined in accordance with ASTM D790 and the results are shown in Table 5, below. Table 5 * = comparative example As can be seen from Table 5, the aramid fiber compounds employing the polyurethane matrix resin of this invention which are molded under high pressure are stronger than similar compounds molded under low pressure. Accordingly, this invention offers aramid fiber composites having improved ballistic properties as well as improved mechanical properties. Accordingly, it can be seen that the present invention offers a method for making ballistic structures of aramid compound having improved ballistic properties, such as ballistic impact resistance to high energy rifle bullets, when casting under high pressure in comparison with molded structures under low pressure. In addition, the same improvements are not observed with the use of other matrix resins. Having described the present invention in a manner relatively detailed, it will be understood that it is not necessary to strictly adhere to such details but that additional changes and modifications may occur to a person skilled in the art and all of them fall within the scope of the present invention defined in the appended claims.

Claims (35)

1. CLAIMS 1. A method for manufacturing a ballistic impact resistant composite having improved resistance to bullets of high energy rifles and the like, said method comprising: providing at least one fibrous layer comprising a high aramid fiber network. tenacity; coating the fibrous layer with a thermoplastic polyurethane resin; and molding the fibrous layer at a pressure of at least about 10.3 MPa (1,500 psi).
2. 2. The method according to claim 1, wherein at least two fibrous layers are provided, each of said fibrous layers comprises a network of high tenacity aramid fibers, and said method further comprises the fact of coating each one. of said fibrous layers with a thermoplastic polyurethane resin, and molding said fibrous layers at a pressure of at least about 10.3 MPa (1,500 psi).
3. 3. The method according to claim 2, wherein said fibrous layers are molded at a pressure of at least about 13.8 MPa (2,000 psi).
4. 4. The method according to claim 2, wherein said fibrous layers are molded at a pressure of at least about 20.7 MPa (3,000 psi).
5. 5. The method according to claim 2, wherein said fibrous layers are molded at a temperature from about 24 to about 127 ° C (75 to 260 ° F).
6. The method according to claim 2, wherein said thermoplastic polyurethane resin is present in an amount of about 1 to about 40 weight percent of the total weight of the compound.
7. The method according to claim 2, wherein said thermoplastic polyurethane resin is present in an amount of about 10 to about 30 weight percent of the total weight of the compound.
8. The method according to claim 2, wherein adjacent fibrous layers are cross-folded in relation to each other.
9. The method according to claim 8, wherein each of said fibrous layers comprises a non-woven fabric wherein said fibers are arranged unidirectionally in each layer.
10. The method according to claim 9, wherein adjacent fibrous layers of said fibers in said fibrous non-woven layers are unidirectionally placed in each layer.
11. The method according to claim 10, wherein said fibrous layers are cross-folded at 90 ° to each other.
12. 12. The method according to claim 2, further comprising at least one plastic film in contact with at least one of said fibrous layers.
13. A method for manufacturing a ballistic impact resistant composite having improved resistance to high energy rifle bullets and the like, said method comprising: supplying a first fibrous layer comprising a network of high tenacity aramid fibers; coating said first fibrous layer with a first thermal polyurethane resin; providing a second fibrous layer comprising a network of high tenacity aramid fibers; coating said second fibrous layer with a second thermoplastic polyurethane resin; and molding said first fibrous layer and said second fibrous layer at a pressure of at least about 10.3 MPa (1, 500 psi).
14. 14. The method according to claim 13, wherein each of said fibrous layers comprises a non-woven fabric.
15. The method according to claim 14, wherein said fibers in each of said first fibrous layer and said second fibrous layer are unidirectionally placed in each layer.
16. 16. The method according to claim 15, wherein said fibrous layers are cross-folded at 90 ° to each other.
17. 17. The method according to claim 14, wherein said fibrous layers are molded at a pressure of at least about 13.8 MPa (2)., 000 psi).
18. 18. The method according to claim 14, wherein said fibrous layers are molded at a pressure of at least about 20.7 MPa (3,000 psi).
19. The method according to claim 14, wherein said fibrous layers are molded at a temperature of about 24 to 127 ° C (75 to 260 ° F).
20. The method according to claim 16, wherein said first thermoplastic polyurethane resin and said second thermoplastic polyurethane resin are present in an amount of about 1 to about 40% by weight of the total weight of each of said layers.
21. The method according to claim 20, wherein said first thermoplastic polyurethane resin and said second thermoplastic polyurethane resin are the same polyurethane resin.
22. 22. The method according to claim 21, wherein said polyurethane resin comprises a copolymer mixture of polyurethane resins.
23. 23. The method according to claim 21, wherein said fibers in said first fibrous layer and said second fibrous layer have a tenacity of at least about 20 g / d.
24. The method according to claim 23, wherein said fibers in said first fibrous layer and said second fibrous layer have a denier of about 200 to about 3,000.
25. 25. The method according to claim 23, further comprising at least one plastic film in contact with at least one of said fibrous layers.
26. 26. An article formed by the method of claim 13.
27. 27. A method for manufacturing a ballistic impact resistant composite having improved resistance to high energy rifle bullets and the like, said method comprising: providing a first fibrous layer nonwoven comprising a network of high tenacity aramid fibers; coating said first nonwoven fibrous layer with a first thermoplastic polyurethane resin; providing a second fibrous nonwoven layer comprising a network of high tenacity aramid fibers; coating said second fibrous non-woven layer with a second thermoplastic polyurethane resin; arranging said first nonwoven fibrous layer and said second nonwoven fibrous layer in such a manner that said first nonwoven fibrous layer and said second nonwoven fibrous layer are oriented relative to one another; and molding the first fibrous layer and the second fibrous layer at a pressure of at least about 10.3 MPa (1,500 psi).
28. The method according to claim 27, wherein said fibrous layers are molded at a pressure of at least about 13.8 MPa (2,000 psi), wherein said fibers in each of said first fibrous layer and said second fibrous layer they are positioned unidirectionally in each layer, and wherein said fibrous layers are cross-folded at 90 ° to each other.
29. 29. The method according to claim 28, wherein said first thermoplastic polyurethane resin and said second thermoplastic polyurethane resin are present in an amount of about 10 to about 30 weight percent of the total weight of each of said layers.
30. 30. An article formed by the method of claim 29.
31. 31. A method for improving the resistance of a ballistic impact-resistant body armor to bullets of high-energy rifles and the like, said method comprising: providing at least one first fibrous layer comprising a network of high tenacity aramid fibers; coating said first fibrous layer with a first thermoplastic polyurethane resin; providing at least a second fibrous layer comprising a network of high tenacity aramid fibers; coating said second fibrous layer with a second thermoplastic polyurethane resin; molding said first fibrous layer and said second fibrous layer at a pressure of at least about 10.3 MPa (1,500 psi) to form a molded article; and forming the body armor at least in part of said molded article.
32. 32. The method according to claim 31, comprising at least about 40 pairs of fibrous layers, each of which comprises a network of high tenacity aramid fibers; coating each of said fibers with a thermoplastic polyurethane resin; and molding said fibrous layers at a pressure of at least about 10.3 MPa (1,500 psi) to form said molded article.
33. The method according to claim 32, wherein said fibrous layers comprise non-woven fabrics whose fibers are unidirectionally placed in each layer, and wherein said fibrous layers are cross-folded at 90 ° between them.
34. 34. The method according to claim 33, further comprising at least one plastic film in contact with at least one of said fibrous layers.
35. 35. A ballistic impact resistant armor article formed by the method of claim 34.