BALLISTIC LAMINATE COMPRISING AT LEAST TWO PAIRS OF UNIDIRECTIONAL LAYERS, WITH FIBERS PARALLEL TO EACH OTHER AND SEPARATED BY A CONNECTING LAYER

Abstract

The present invention relates to a structure for the construction of ballistic protection that combines high projectile-stopping and trauma-reduction performance with high flexibility. A ballistic laminate comprising at least two pairs of unidirectional layers, with fibers parallel to each other, separated by a connecting layer, is produced. In a preferred embodiment, the ballistic structure includes a plurality of unidirectional ballistic yarn sublaminates Each sublaminate comprises at least two unidirectional ballistic layers whose fibers are substantially parallel, i.e. oriented in the same direction; the two ballistic layers with parallel fibers are not in direct contact with each other but are separated (and held together) by a layer consisting, for example, of a film which is also adhesive. The sublaminates are then coupled together so that the unidirectional fibers of each sublaminate are substantially perpendicular to those of the adjacent sublaminate.

Claims

1. Ballistic laminate for ballistic protection, the laminate comprising at least a first unidirectional textile sub-laminate and at least a second unidirectional textile sub-laminate, each of the first and second textile sub-laminate comprising a first textile layer having a first plurality of ballistic fibers arranged in a direction α and a second textile layer comprising a second plurality of ballistic fibers arranged substantially according to the direction α, the first and second textile layers of each sub-laminate being separated by a connecting layer, the first and second sub-laminate being in direct contact with each other and arranged so that the direction of the fibers of the first sub-laminate and the direction of the fibers of the second sub-laminate form a relative angle of 90°+/−10°.

2. Ballistic laminate according to claim 1, wherein the textile layers are pre-impregnated by a matrix of resin comprising one or more of the following materials: acrylic, polyethylene, polybutene, polyurethane resins based on block copolymers.

3. Ballistic laminate according to claim 1, in which the connecting layer comprises one or more of the following materials: polyurethane, polyester, polyamide, polyethylene, polypropylene, in the form of a film or other structure, such as nets, felts or fabric woven/non-woven.

4. Ballistic laminate according to claim 1, wherein the ballistic fibers comprise one or more of the following materials: aramid, polyamide, high-molecular-weight polyethylene UHMWPE, copoliaramidic, polybenzoxazole, polybenzothiazole, liquid crystals, glass, carbon.

5. Ballistic laminate according to claim 1, comprising a plurality of through holes having a diameter between 0.02 mm and 3 mm, the through holes passing through the first and second sub-laminate and having a density between 0.5 and 10 per cm.sup.2.

6. Ballistic laminate according to claim 1, wherein the first and second sub-laminate are joined each other by means of pressing action.

7. Ballistic laminate according to claim 6 wherein the through holes are made after the pressing action.

8. Ballistic laminate according to claim 5 wherein the first and second sub-laminate are joined together by means of sewing and at least part of the through holes are made during the sewing.

9. Ballistic laminate according to claim 8, wherein the seam is made by means of needles having a diameter at least 20% greater than the diameter of the yarn used for sewing.

10. Ballistic protection comprising at least one ballistic laminate of claim 1.

11. Process of manufacture of a ballistic laminate of claim 1, comprising the steps of: arranging at least a first unidirectional textile layer, a connecting element and at least a second unidirectional textile layer in contact with one another so that the connecting element is interposed between the textile layers and keeps them joined together, the first and the second textile layer comprising a plurality of ballistic fibers disposed substantially in the same direction (+/−10°); joining the at least first textile layer, the connecting element and the at least second textile layer to each other by pressure, obtaining a textile sub-laminate; arranging a first textile sub-laminate and a second textile sub-laminate in contact with one another so that the direction of the fibers of the first textile sub-laminate and the direction of the fibers of the second textile sub-laminate have a relative angle of 90°+/−10°; joining the at least first sub-laminate and the at least second sub-laminate together by means of a pressure between 1 and 200 bar.

12. A hybrid ballistic package comprising: at least one ballistic laminate according to claim 1 based on polyethylene UHMW fibers with a toughness (tenacity) higher than 30 cN/dtex, a modulus higher than 120 Gpa and an elongation higher than 2%; and at least one layer of aramid copolymer-based fabrics having fiber toughness (tenacity) greater than 26 cN/dtex, modulus greater than 100 Gpa and elongation greater than 2% so that: the specific energy absorbed with 55 grs fsp is higher than 35 j/kg/m.sup.2 the ratio between the V50 with 0.44 Magnum Speer HP bullet according to the NIJ0.101.06 standard of a package weighing less than 4.6 kg/m.sup.2 and the maximum trauma recorded according to NIJ0.101.06 standard is higher or equal to 11 (m/s)/mm.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0042] These and further advantages, objects and characteristics of the present invention will be better understood by a person skilled in the art from the description below and the attached drawing relating to embodiments of an illustrative character, but not to be understood in a limiting sense, in which:

[0043] FIG. 1 shows a perspective view of a structure for ballistic protection according to a possible embodiment of the present invention, before the holes are drilled;

[0044] FIG. 2 shows a side view of the structure in FIG. 1;

[0045] FIG. 3 diagrammatically illustrates the inflection (or discontinuity) in the straight line direction of the unidirectional fibers caused by the through holes.

DETAILED DESCRIPTION

[0046] According to a preferred embodiment of the present invention there is provided a structure comprising a plurality of unidirectional ballistic yarn sublaminates. Each sublaminate comprises at least two unidirectional ballistic layers having substantially parallel fibers, i.e. oriented in the same direction; the two ballistic layers with parallel fibers are not in direct contact with each other, but are separated (and held together) by means of a layer consisting for example of a film, which may be adhesive.

[0047] The sublaminates are then joined together so that the unidirectional fibers of each sublaminate are substantially perpendicular to those of the adjacent sublaminate.

[0048] As shown in FIG. 1 the structure comprises an overlapping of layers composed as follows: [0049] layer 101 of unidirectional fibers in direction α (e.g. 0°), preferably impregnated with a matrix (e.g. a matrix having a low modulus and high elongation); [0050] layer 105 of adhesive polymer structure, such as film, mesh, etc.; [0051] unidirectional fiber layer 101 in direction α (parallel and NOT in the 13 direction (in the present example 90°), perpendicular to the a direction, as in solutions in the known art) impregnated with a matrix (for example having a low modulus and high elongation); [0052] unidirectional fiber layer 103 in direction 13 perpendicular to direction α; [0053] layer 105 of adhesive polymeric structure such as film, mesh, etc.; [0054] unidirectional fiber layer 103 in the 13 direction (and NOT in the a direction perpendicular to the 13 direction) impregnated with a matrix.

[0055] In the structure in FIG. 1 the three upper layers 101, 105 and 101 constitute the first sublaminate with fibers (of layers 101) all oriented in the same direction α; the three lower layers 103, 105 and 103 constitute the second sublaminate in which the ballistic fibers (of layers 103) are all oriented in the 13 direction perpendicular to a.

[0056] One characteristic of this structure is that the unidirectional ballistic fiber layers are arranged so that they form sub-sets of layers (in our example pairs, but could be more than two) with parallel fibers (first layer 101 with second layer 101; first layer 103 with second layer 103) and the parallel pairs are separated by adhesive elements (e.g. adhesive films) 105. On the contrary, the pairs of adjacent layers with fibers perpendicular to each other (second layer 101 and first layer 103, preferably impregnated with a matrix), in a preferred embodiment of the present invention are in direct contact with each other, without a protective film in between. This characteristic of direct contact increases the ballistic performance of the structure.

[0057] For simplicity in this description we refer to precise measurements and definitions (e.g. 0° and 90° or parallel and perpendicular), but for the purposes of this invention it is intended that such measurements and definitions should be taken with a certain degree of approximation, so 0° means 0°+/−10°; 90° means 90°+/−10°, parallel means “substantially parallel” and perpendicular means “substantially perpendicular”. FIG. 2 shows the same structure as FIG. 1 in side view where the sequence of layers (101+105+101+103+105+103) can be seen and once again shows that the adhesive film separates the layers with fibers parallel to each other (or rather substantially parallel), but not those with fibers perpendicular to each other (substantially perpendicular).

[0058] The ballistic layers according to a preferred embodiment of the present invention are made of ballistic yarns arranged unidirectionally in the directions indicated above. Small plates or monofilaments may be used as an alternative to yarns generally composed of numerous filaments. The yarn counts of these yarns (plates, monofilaments) are advantageously between 20 and 6500 d/tex, their tenacity is higher than 10 cN per d/tex, the modulus is higher than 40 GPa and tensile elongation is between 1% and 10%; for example, aramid yarns produced by Teijin®, DuPont®, Kolon®, Hyousung®, with the trade names of Twaron®, Kevlar®, Heracron®, Alkex®, belong to these classes.

[0059] In addition to aramid yarns, ultra-high molecular weight P.E. yarns may be used, for example those produced by Honeywell®, DSM®, with the trade names Spectra® and Dyneema® respectively, also in the form of plates known under the trade names Tensylon® or Endumax®. Recently copolyaramide yarns have been introduced under the names of Ruslan®, Rusar®, Autx®, Artec, produced by Kamenksvolokno®. These yarns are characterized by a dynamic tensile strength of at least twice the static strength, thus allowing high ballistic performance.

[0060] Preferably, the layers of ballistic yarns that make up the ballistic structure according to the present invention are pre-impregnated with thermoplastic and thermosetting resins, including mixtures thereof; the mechanical nature of these resins can be elastomeric, plastomeric, visco-elastic, etc. Among these, acrylic polyethylene, polybutenic, polyurethane resins based on block copolymers (styrene-butadiene-styrene type), also known by the commercial term Kraton, are particularly useful.

[0061] The quantities applied are between 3% and 30%. The purpose of applying the resin is to facilitate adhesion between the various layers of unidirectionally deposited and superimposed yarns. In addition, the resins put the various fibrils of the yarns in close contact, creating a continuity useful for ballistic purposes. As described above, additional elements (105) are applied between each pair of unidirectional “parallel” ballistic layers (e.g. 101 and 101 in FIG. 1 and FIG. 2) in order to stabilize the structure and protect the yarn fibrils from a mechanical action resulting from the mutual rubbing of the layers during use. Elements 105 may also be discontinuous films, felts, mesh and non-woven fabrics.

[0062] The composition of these layers 105 (e.g. film) must allow adhesion between the layers. Thus elements based on thermoplastic and thermosetting polymers, including mixtures thereof, are used. The mechanical nature of these resins may be elastomeric, plastomeric, viscoelastic, etc. Polyethylene, polyurethane, polycarbonate, polyamide, polypropylene and polyester films, also in the form of copolymers, are for example particularly useful. Advantageously the weights of these additional elements should be as low as possible, ideally around 3 g/m.sup.2. The structure thus obtained is subjected to the action of pressure and temperature. The pressures are advantageously between 2 and 200 bar and more advantageously between 20 and 40 bar. The pressing temperatures are between 20° and 200° C. and more advantageously between 30° and 110° C. The pressure/temperature combination is applied using processes known to those skilled in the art and may be both continuous and discontinuous. The laminate so obtained undergoes a further process phase comprising creating discontinuities throughout the entire structure of the laminate.

[0063] Ballistic tests have shown that for the same mass of ballistic protection the better? performance is obtained the lower the weight of the single layer of protection.

[0064] The ideal ballistic structure should therefore have the following characteristics:

[0065] 1. fiber with high tensile properties (high tenacity, high elongation, high modulus)

[0066] 2. a single layer of limited weight,

[0067] 3. suitable resin impregnating the individual unidirectional fibers

[0068] 4. low-weight film placed between adjacent layers with fibers parallel to each other to limit relative movement between the fibers of adjacent layers having a tenacity of at least 20 MPa and an elongation at break of more than 500%,

[0069] for example ballistic fabric of total weight 100 g/m.sup.2, comprising 4 unidirectional layers of about 22 g/m.sup.2, between which a 3 g/m.sup.2 film is placed.

[0070] As mentioned above, the best way to block movement between the fibers of the adjacent layers with fibers parallel to each other during use is to use an adhesive film.

[0071] While the single layer can be made almost as light as desired, the film has limits to lightness beyond which it is not possible to go because of production problems.

[0072] The invention described above can be used to produce unidirectional fiber layers of any low weight connected to each other for example by means of film; the film connecting the unidirectional layers which are not rotated with respect to each other offers a weak interaction in comparison with the situation where the film is placed between layers rotated with respect to each other; contrary to what might be imagined this “weak” interaction effect is positive.

[0073] Film stabilization of the unidirectional fiber layers that are not rotated also makes it possible to avoid the further application of film on the outer surfaces of the final structure as strength is guaranteed by the film (or other separating element) itself present between the layers.

[0074] The structure described above, which is theoretically contrary to the normal rules of construction according to the techniques in the known art, instead offers performance that combines high V50 and low trauma.

[0075] If through holes passing through the entire structure are made in order to give greater flexibility to the unidirectional laminated structure, undulations and therefore inflections (or discontinuities) in the straight course of the ballistic yarns are created, as shown in FIG. 3. It has been surprisingly established that the flexibility characteristics of the structure are greatly improved through the presence of these inflections, as are the breathability characteristics, without compromising the ballistic characteristics in terms of both stopping power and magnitude of trauma induced by the impact energy. The number of these through holes and their diameter can be adapted to the needs of each individual structure (to increase or decrease flexibility and breathability). Advantageously, the holes preferably have a substantially circular shape (but may also be of other, for example elliptical, shapes); in a preferred embodiment of the present invention the diameter of these holes is between 0.02 mm and 3 mm, preferably between 0.5 and 2 mm. The number of such through holes (i.e. their density) is preferably between 0.1 and 10 per cm.sup.2, more preferably between 0.5 and 10 per cm.sup.2.

[0076] In a preferred embodiment, the various layers of the laminate are stitched together and it is precisely the stitching operation that creates the through holes.

[0077] It is preferable that the diameter of the stitching thread be 20% to 90% smaller than the diameter of the through holes created by the needle or latch that provides this type of stitching. This stitching thread is selected according to the structure and weight of the laminate to be made. The stitching thread count is advantageously between 20 d/tex and 300 d/tex. Threads based on organic polymers such as polyester, polyamides, polyethylene, polypropylene, or inorganic threads such as basalt, carbon, glass, are used. The nature of the stitching is not decisive for the performance of the laminate. In some cases, when the diameter of the stitching thread is much smaller than the diameter of the hole/channel created and especially with certain types of stitching, the thread is not locked and therefore easily “removable”, thus ceasing to play its part. In this case, a two-component monofilament is used for the stitching itself, in which the outer part can be melted more easily than the inner part, the melting point of which is much higher so that it remains intact during the pressing stage at its temperature. In a preferred form of embodiment, the needles (e.g. the crochet) are fed by non-ballistic threads that pass perpendicularly through all the layers of the laminate, thus increasing the cohesion between the various layers of the laminate after being properly knotted with a knitted or chain knot.

[0078] The length of the binding stitch is advantageously between 1 and 20 mm and the distance between the various stitching threads in the longitudinal direction is advantageously between 1 and 20 mm.

[0079] Devices and machines known to those skilled in the art, which may possibly be suitably modified, such as quilting machines or multiple head sewing machines, may be used to make the seams.

[0080] As mentioned, stitching of the structure is optional and is not necessarily linked to the existence of the through holes described above. The presence of the through holes, which can be obtained by alternative methods if there is no stitching operation, nevertheless provides the above-mentioned advantages of increased flexibility and breathability. One of the alternative methods for making the through holes and the relative discontinuities in the rectilinear direction of the fibers (i.e. without the stitching stage) consists of subjecting the laminate to the action of a series of punches placed on a rotating cylinder suitably loaded to exert the pressure needed to perforate the laminate so that the punches penetrate through the entire thickness of the laminate.

[0081] In an optional embodiment of the present invention, it is also possible for the two techniques, i.e. both stitching and punching (or other technique to produce through holes), to coexist: in this case some holes will have the stitching thread within them, while others will not.

[0082] For a better description of the contents of this invention, FIG. 3 shows the undulation that is created in the yarn placed unidirectionally following penetration by the needle, punch or latch. The creation of these discontinuities must not cause any damage to the ballistic fibers. The punches, crochets or needles that create such discontinuities must not therefore have sharp edges or sharp parts, but must be suitably rounded.

[0083] The structure of the laminate comprises at least two sublaminates, each comprising a pair of layers of prepreg yarns, the individual layers having the fibers parallel to each other and separated from each other by a protective film; the at least two sublaminates are superimposed, with the direction of the unidirectional yarns in each sublaminate oriented at an angle of 90°+/−10° with respect to the adjacent sublaminate.

[0084] In a preferred embodiment, the number of layers of a single laminate is 4 (two for each sublaminate), but may also be greater, for example any multiple of 2, for example 8.

[0085] Ballistic protection made from laminate according to the present invention may include a variable number of laminate structures described above, preferably ranging from a minimum of 1 to a maximum of 50.

[0086] The structure which is the subject matter of the present invention may be further improved by applying an additional treatment that drastically increases the flexibility of the structure; this improvement is caused by an ordered reduction in thickness along the entire length of the piece, created during the optional stage of stitching the layers together.

[0087] These reductions in thickness may be in the same direction as the piece or at 45° to the direction of the length of the piece or a combination thereof.

[0088] The best performance is obtained when the reductions in thickness are discontinuous, interrupted by holes in which binding elements e) are inserted; these holes also have the valuable effect of deflecting from the straightness of the ballistic fiber, having a favorable effect on the elongation at break of the fiber itself and increasing its ballistic properties (Cunniff's formula on elongation).

[0089] The channels have a width of between 0.1 and 1 mm and a length of between 1 and 30 mm.

[0090] The reduction in thickness is obtained by passing the assembly through a further pressing in which the stitching thread makes an impression in the fabric leaving a channel. The pressing creates a reduction in thickness alternating with holes through which thread e) is threaded. Effectively an alternation of channels/threaded holes.

[0091] In the case of unidirectional polyethylene-based fiber layers, for this to happen it is necessary that the binding element should have a higher softening temperature than the ballistic fiber and that the ballistic fiber should allow itself to be deformed plastically.

[0092] It is also preferable that there should be no adhesion between the binding element and the reduction in thickness (otherwise ballistic fibers are locked) and that there should be adhesion between the film positioned between the two adjacent layers of unidirectional fibers directed in the same direction and the binding element. This ensures that the binding element is cohesive with the structure and cannot slip out during subsequent cutting into vest shapes.