Protective woven fabric

Abstract

Protective woven fabric comprising interwoven warp tapes and weft tapes, each tape extending along a respective extension direction and being made at least in part with UHMWPE film, wherein each tape comprises at least a first UHMWPE film layer and a second UHMWPE film layer stacked and j oined to each other in such a way that the respective polymeric chains are oriented substantially parallel to the corresponding extension direction.

Description

[0001] PROTECTIVE WOVEN FABRIC

[0002] The present invention refers to a protective woven fabric, and in particular to a woven fabric made with interwoven UHMWPE film tapes.

[0003] The present invention relates to the field of materials used for the production of protective articles, and in particular articles for ballistic protection, i.e. articles having properties of resistance to penetration by bullets, fragments, splinters and blades, or more in general articles capable of protecting against shocks and impacts .

[0004] Ballistic protection materials known in the state of the art are generally made with a plurality of protective fabrics stacked and joined to each other until they reach predetermined area density values (measured in grams per square metre) .

[0005] These fabrics generally comprise ballistic fibre yarns interwoven as weft yarns and warp yarns, wherein such ballistic fibres are characterized by high strength, high tenacity, and high elastic modulus. Ballistic fibres include for example aramid fibres, para-aramid fibres or ultra high molecular weight poly-ethylene (UHMWPE') based fibres.

[0006] Alternatively, a ballistic protection material made with a plurality of UHMWPE film sheets stacked and joined to each other has recently been developed. In particular, the UHMWPE film is formed by extruding and stretching a compacted starting block of UHMWPE, obtaining a film with a width comprised between 80 centimetres and 160 centimetres in which the UHMWPE polymer chains are oriented along a same extension direction: in fact, it has been observed that, as the stretching of the film increases, and therefore as the relative thickness decreases, a greater alignment of the polymer chains is obtained, and therefore also a greater mechanical resistance. The UHMWPE film sheets thus obtained are then stacked until they reach predetermined area density values (measured in grams per square metre) , usually in groups of four and necessarily in such a way that the extension directions of the adjacent sheets are perpendicular to each other (they are defined as "crisscross" sheets) , and joined to each other by interposing thermoplastic polymer layers and executing a moulding of the material at a pressure of at least 55 bar.

[0007] This material made with "criss-cross" UHMWPE film sheets proved to be characterised by a greater mechanical and ballistic resistance compared to the materials made with similar ballistic fibre fabrics (i.e. based on UHMWPE) , and also more resistant to ageing. However, the process to produce this material is long, complicated and expensive. In fact, the fact that the moulding must, in order to be effective, be carried out at least at 55 bar, makes it necessary to use a press, with all the costs related to the purchase and maintenance of the tool and the relative equipment (including the moulds) , and with the long times that are necessary to use it safely .

[0008] The material made with "criss-cross" UHMWPE film sheets is also characterized by a poor "drapability", that is, a poor ability to adhere to objects of complex shape once moulded.

[0009] In addition, the stacking operation (called "crisscross" stacking) of the UHMWPE film sheets in such a way that the extension directions of the adjacent sheets are perpendicular to each other is very complex, and requires the use of special expensive and bulky machines. In fact, since the UHMWPE film is formed by extruding and stretching a compacted starting block of UHMWPE, it is necessary to cut this film into sheets and then rotate one sheet every two by 90° before stacking it on the underlying sheet .

[0010] With the aim of overcoming the drawbacks of the material made with "criss-cross" UHMWPE film sheets, while maintaining the advantageous characteristics listed, the Applicant has developed a protective material made with a plurality of protective fabrics stacked and joined to each other, where each fabric comprises interwoven UHMWPE film tapes instead of yarns of ballistic fibres. In particular, each tape is formed by cutting a UHMWPE film sheet along the relative extension direction, so that the UHMWPE polymer chains are oriented along the extension direction of the tape, and the tapes thus obtained are woven avoiding twists to form the woven fabric. The woven fabrics are then stacked and joined to each other until they reach predetermined area density values, interposing thermoplastic polymer layers and executing a moulding at a pressure not exceeding 10 bar. In fact, the Applicant observed how the material made with woven fabrics of UHMWPE film tapes can also be produced with a moulding at a pressure not exceeding 10 bar, while obtaining the same resistance characteristics of the material made with "criss-cross" UHMWPE film sheets, i.e. greater mechanical, ballistic and ageing resistance compared to the materials made with similar ballistic fibre fabrics. This makes it possible to use an autoclave for moulding, instead of a press, i.e. to use equipment that is much cheaper to buy and execute maintenance thereon, and that can be used more easily and quickly.

[0011] In addition, it was observed that the material made with woven fabrics of UHMWPE film tapes is characterized by better drapability than the material made with "crisscross" UHMWPE film sheets.

[0012] The Applicant therefore dealt with the further problem of forming a protective material that, with the same area density, could be formed even faster than the material made with woven fabrics of UHMWPE film tapes, while maintaining all the advantageous characteristics observed, i.e. greater mechanical, ballistic and aging resistance (hereinafter referred to as a whole as "resistance characteristics") compared to the materials made with similar ballistic fibre fabrics, and a better drapability compared to the material made with "crisscross" UHMWPE film sheets.

[0013] These and other results are obtained according to the present invention as illustrated in the following description .

[0014] In particular, the invention relates to a protective woven fabric, which stacked on itself a certain number of times composes a protective material usable for the production of protective articles, and in particular articles for ballistic protection, i.e. articles having properties of resistance to penetration by bullets, fragments, splinters and blades, or more in general articles capable of protecting against shocks and impacts .

[0015] The fabric consists of UHMWPE film tapes interwoven as weft tapes and warp tapes perpendicular to each other. Each tape extends along a respective extension direction, and is made at least in part with UHMWPE film (which can be formed according to known processes) .

[0016] More in detail, each tape comprises at least a first UHMWPE film layer and a second UHMWPE film layer stacked and joined to each other to form the tape itself, in such a way that the UHMWPE polymer chains of both layers are oriented substantially parallel to the extension direction of the tape.

[0017] In this way, the fabric obtained by weaving the tapes formed by two UHMWPE film layers has a thickness that is substantially double and an area density that is substantially double with respect to the fabric obtained by weaving the tapes formed by a single UHMWPE film layer, i.e. with respect to the previous solution devised by the Applicant. Consequently, to reach the predetermined area density value, it is sufficient to stack about half of the fabrics that were previously necessary .

[0018] Furthermore, the total time required to weave the tapes formed by two UHMWPE film layers is substantially identical to the time required to weave the tapes formed by a single UHMWPE film layer, as the total number of weft tapes and warp tapes remains unchanged. Consequently, the time required as a whole to form a single fabric is substantially identical to the Applicant' s previous solution, while on the contrary the overall time required to form a protective material having a predetermined area density value is approximately halved compared to that previously necessary . Each tape may further comprise a third UHMWPE film layer stacked on and joined to the first layer and / or the second layer, in such a way that the UHMWPE polymer chains of the third layer are also oriented substantially parallel to the extension direction of the tape. In this way, the fabric obtained by weaving the tapes formed by three UHMWPE film layers is substantially three times as thick and has substantially three times the area density of the fabric obtained by weaving the tapes formed by a single UHMWPE film layer. Consequently, to reach the predetermined area density value, it is sufficient to stack about one third of the fabrics that were previously necessary, and therefore the protective material can be formed in about one third of the time compared to before. It was also observed that, with the same thickness of the tapes and therefore the same area density of the fabric, the fabric obtained by weaving the tapes formed by several UHMWPE film layers has better resistance characteristics than the fabric obtained by weaving the tapes formed by a single UHMWPE film layer. In fact, the more a UHMWPE film is stretched and thin, the more the polymer chains that compose it are aligned with each other, giving it better resistance characteristics. Therefore, a tape of a certain thickness made with several thin UHMWPE film layers has better resistance characteristics than a tape with the same thickness made with a single thicker UHMWPE film layer.

[0019] Each tape can also comprise further UHMWPE film layers stacked and joined to the other UHMWPE film layers, always in such a way that the respective UHMWPE polymer chains are oriented substantially parallel to the extension direction of the tape. However, preferably the number of UHMWPE film layers is not greater than three, in order to facilitate the weaving operation in which the tapes are woven to form the fabric.

[0020] In any case, the tapes are interwoven with each other without twists, that is, without even partial rotations of the tapes on themselves around the extension direction. In this way, the fabric is completely homogeneous and free of defects.

[0021] The UHMWPE film layers of each tape are joined to each other by interposing thermoplastic polymer layers, preferably LLDPE or HDPE, which act as a glue. In particular, each thermoplastic polymer layer may consist of a thermoplastic polymer film having a thickness comprised between 4 micrometres and 10 micrometres, or of an aqueous solution or a powder laid between the UHMWPE film layers (according to techniques known in the art) with an area density comprised between 1.5 grams per square metre and 5 grams per square metre.

[0022] Each UHMWPE film layer has a width comprised between 3 millimetres and 25 millimetres, preferably between 4 millimetres and 6 millimetres. Consequently, this value also represents the width of each tape. Each UHMWPE film layer has a thickness comprised between 4 micrometres and 25 micrometres.

[0023] The weave of the fabric can be chosen from those generally used for the protective woven fabrics, such as for example plain, twill, satin and basket. Preferably the fabric is formed by weaving the weft and warp tapes with 3:1 twill weave, as it has been observed that the woven fabric according to this weave has better resistance characteristics than those of the woven fabrics according to other weaves. In addition, the woven fabric with 3:1 twill weave has demonstrated a greater drapability than the woven fabrics according to other weaves .

[0024] Each woven fabric can be formed according to the invention through a method comprising the following steps :

[0025] - providing at least two UHMWPE film sheets, each of them having the respective UHMWPE polymer chains oriented along a respective extension direction;

[0026] - stacking and joining to each other the UHMWPE film sheets in such a way that the respective extension directions are substantially parallel to each other;

[0027] - cutting the stacked UHMWPE film sheets substantially parallel to the extension directions, obtaining UHMWPE film tapes that extend along the extension direction and are made with several UHMWPE film layers with the respective UHMWPE polymer chains oriented substantially parallel to the extension direction;

[0028] - interweaving the UHMWPE film tapes thus obtained as weft tapes and warp tapes, forming the woven fabric.

[0029] Preferably, the step of stacking and joining to each other the UHMWPE film sheets also comprises the sub-step of interposing thermoplastic polymer layers between the UHMWPE film sheets, serving as a glue.

[0030] Preferably, a top thermoplastic polymer layer is laid in this step also on the top UHMWPE film sheet; in this way each subsequently obtained UHMWPE film tape, and therefore also the woven fabric, has a top thermoplastic polymer layer that is useful for joining the woven fabric with another woven fabric that will be stacked on it.

[0031] It was observed that the step of stacking and joining to each other the UHMWPE film sheets, which is the only additional step with respect to the process for producing the fabric of single-layer tapes, requires a much shorter time than the step of cutting the sheets into tapes and the step of interweaving the tapes with each other. For this reason, as mentioned, the time required as a whole to produce a single fabric is substantially identical to the Applicant previous solution.

[0032] In addition, the operation of stacking the UHMWPE film sheets in such a way that the respective extension directions are substantially parallel to each other is much simpler and faster than the "criss-cross" stacking operation that characterizes the production of the material made with "criss-cross" UHMWPE film sheets, and requires the use of much more compact and economical machines, as no rotation of the UHMWPE film sheets is necessary .

[0033] As already mentioned, the woven fabrics thus produced can be stacked and joined to each other to form a protective composite material according to the invention, having a predetermined area density value. It has been observed that, with the same area density, the material made with the fabrics according to the invention has substantially identical or better resistance characteristics compared to the material made with fabrics of single-layer UHMWPE film tapes. In fact, the overall thickness of UHMWPE film is substantially identical in the two cases, but each single UHMWPE film layer is thinner in the material according to the invention and this, as mentioned, guarantees better resistance characteristics.

[0034] Furthermore, it has been observed that the material according to the invention has a drapability substantially identical to the material made with single-layer tape fabrics.

[0035] The woven fabrics, once stacked, are joined to each other by means of thermoplastic polymer layers, preferably LLDPE or HDPE . In particular, each thermoplastic polymer layer may consist of a thermoplastic polymer film having a thickness comprised between 4 micrometres and 10 micrometres, or of an aqueous solution or a powder laid between the fabrics with an area density comprised between 1.5 grams per square metre and 5 grams per square metre .

[0036] Preferably such thermoplastic polymer layers consist of the top thermoplastic polymer layers of each one of the woven fabrics. Alternatively, additional thermoplastic polymer layers may be specially interposed between the woven fabrics.

[0037] The material according to the invention can be used in so-called "protective packages" (or "ballistic packages") for the production of protective articles, such as for example bulletproof vests, multi-protection vests, helmets, anti-trauma protections, bulletproof plates, panels and rigid cover plates and / or armour for vehicles or buildings (for example for radomes or for components of the radar systems on the airplanes) .

[0038] The material just described can be formed according to the invention through a method comprising the following steps :

[0039] - providing a plurality of woven fabrics according to the invention;

[0040] - stacking the woven fabrics;

[0041] - joining the woven fabrics to each other by means of a moulding . In fact, moulding allows the thermoplastic polymer layers to be partially fused, joining the stacked woven fabrics to each other.

[0042] The moulding is preferably executed at a pressure not exceeding 15 bars, preferably at a pressure of 10 bars. In fact, it has been observed that this pressure is sufficient to join the stacked woven fabrics, giving the material its distinctive resistance characteristics. Preferably, the moulding is executed inside an autoclave. In this way, the production process of the material according to the invention is quick, simple and economical even for objects having complex shape, also thanks to the fact that it is possible to do without a press for the moulding operation.

[0043] The present invention has been described, by way of nonlimiting example, according to preferred embodiments, but it is to be understood that changes and / or modifications may be made by the person skilled in the art, without departing from the relative scope of protection, as defined in the appended claims.

Claims

CLAIMS1) Protective woven fabric comprising interwoven warp tapes and weft tapes, each tape extending along a respective extension direction and being made at least in part with UHMWPE film, characterized in that each tape comprises at least a first UHMWPE film layer and a second UHMWPE film layer stacked and joined to each other in such a way that the respective polymeric chains are oriented substantially parallel to the corresponding extension direction.2) Woven fabric according to claim 1, wherein each tape comprises also a third UHMWPE film layer stacked and joined to the first UHMWPE film layer and / or the second UHMWPE film layer, in such a way that the respective polymeric chains are oriented substantially parallel to the corresponding extension direction.3) Woven fabric according to any one of the preceding claims, wherein the UHMWPE film layers are joined to each other by means of one or more thermoplastic polymer layers, in particular LLDPE or HDPE layers, interposed between them.4) Woven fabric according to claim 3, wherein each thermoplastic polymer layer consists of a thermoplastic polymer film having a thickness comprised between 4 micrometres and 10 micrometres, or of an aqueous solution or a powder laid between the UHMWPE film layers with an area density comprised between 1.5 grams per square metre and 5 grams per square meter.5) Woven fabric according to any one of the preceding claims, wherein the UHMWPE film layers have a width comprised between 3 millimetres and 25 millimetres, preferably between 4 millimetres and 6 millimetres.6) Woven fabric according to any one of the preceding claims, wherein the UHMWPE film layers have a thickness comprised between 4 micrometres and 25 micrometres.7) Woven fabric according to any one of the preceding claims, wherein the warp tapes and weft tapes are interwoven with each other with 3:1 twill weave.8) Woven fabric according to any one of the preceding claims, wherein the warp tapes and weft tapes are interwoven with each other without twists.9) Composite protective material comprising a plurality of woven fabrics according to any one of claims 1 to 8, the woven fabrics being stacked and joined to each other.10) Composite material according to claim 9, wherein the woven fabrics are joined to each other by means of thermoplastic polymer layers, in particular LLDPE or HDPE layers .11) Composite material according to claim 10, wherein each thermoplastic polymer layer consists of a thermoplastic polymer film having a thickness comprised between 4 micrometres and 10 micrometres, or of an aqueous solution or a powder laid between the UHMWPE film layers with an area density comprised between 1.5 grams per square metre and 5 grams per square meter.12) Method for forming a woven fabric according to any one of claims 1 to 8, comprising the steps:- providing at least two UHMWPE film sheets having polymeric chains oriented along respective extension directions ;- stacking and joining to each other the UHMWPE film sheets in such a way that the respective extension directions are placed substantially parallel;- cutting the UHMWPE film sheets substantially parallelto the extension directions obtaining UHMWPE film tapes;- interweaving the UHMWPE film tapes as warp tapes and weft tapes.13) Method according to claim 12, wherein the step of stacking and joining to each other the UHMWPE film sheets comprises the first sub-step of interposing thermoplastic polymer layers between the UHMWPE film sheets .14) Method according to claim 13, wherein the step of stacking and joining to each other the UHMWPE film sheets comprises the second sub-step of laying a top thermoplastic polymer layer on a top UHMWPE film sheet.15) Method for forming a composite material according to any one of claims 9 to 11, comprising the steps:- providing a plurality of woven fabrics according to any one of claims 1 to 8;- stacking the woven fabrics;- joining the woven fabrics to each other by means of a moulding .16) Method according to claim 15, wherein the moulding is executed at a pressure not exceeding 15 bars, preferably at a pressure of 10 bars.17) Method according to claim 16, wherein the moulding is executed inside an autoclave.18) Method for forming a composite material according to any one of claims 9 to 11, comprising the steps:- providing a plurality of woven fabrics formed through a method according to claim 14;- stacking the woven fabrics;- joining the woven fabrics to each other by means of a moulding .