IT202300002268A1 - METHOD FOR PREPARING A COMPOSITE MATERIAL FOR BALLISTIC PROTECTION IN THE FORM OF A FLEXIBLE SHEET AND RELATED COMPOSITE MATERIAL OBTAINABLE WITH SAID METHOD. - Google Patents

Description

METHOD FOR PREPARING A COMPOSITE MATERIAL FOR BALLISTIC PROTECTION IN THE FORM OF A FLEXIBLE SHEET AND RELATED COMPOSITE MATERIAL OBTAINABLE WITH SAID METHOD

The present invention relates to a method for preparing a composite material for ballistic protection in the form of a flexible sheet and the related composite material obtainable with said method.

The present invention originates in the sector of materials used for the production of articles for ballistic protection, i.e. articles having properties of resistance to the penetration of bodies, such as bullets, splinters, blades, etc.

Articles for ballistic protection known in the state of the art generally comprise a plurality of superimposed layers of ballistic fabrics. Ballistic fabrics are textile substrates comprising ballistic fibres, i.e. fibres having high resistance, tenacity and elastic modulus. These fibres, also known as high performance fibres, include, for example, aramid, para-aramid, polyethylene or other synthetic fibres. In textile substrates, the fibres or yarns comprising said fibres can be bonded together in various ways, so as to form for example a warp and woof fabric, a non-woven fabric (TNT), a unidirectional or multidirectional fabric and others.

Overlapping layers of ballistic fabrics (also called ?ballistic packages?) can be held together in various ways, for example: through stitching, by laminating the fabrics together using thermoplastic films or by impregnation with binding polymeric materials (e.g. thermoplastic or thermosetting resins).

In general, the number of layers of ballistic fabrics that make up a ballistic package varies depending on the type and level of protection sought for the final article (e.g. bulletproof, knife-proof, multi-protection, etc.), the type of ballistic fiber and the ways in which the article is used (e.g. wearable protective articles, rigid protective screens, etc.).

For the manufacture of bulletproof vests, for example, a multilayer package comprising 20 to 50 layers of ballistic fabric is generally used. In particular, in the case of bulletproof vests of protection class SK1 (Technische Richtlinie Ballistische Schutzwesten (2009)), i.e. capable of stopping steel-jacketed bullets (e.g. 9 mm DM41 bullets,.), the most effective textile-based solution currently known in the state of the art is based on the use of a ballistic package comprising at least 36 layers of a light ballistic fabric (approx.

100 - 150 g/m<2>) having a warp/weft type weave (plain) and a fabric density (Walz) - as defined below - greater than 20%, generally in the range 22% - 30%.

The high fabric density of the layers of the ballistic package gives the final product the ability to absorb and disperse the kinetic energy of the projectile. Furthermore, the high Walz fabric density makes the fabric layers adequately processable, i.e. the individual fabric layers can easily be subjected to the cutting to size and packaging operations of the ballistic package (e.g. stacking of the layers), typically carried out by automated machinery, avoiding in particular the fraying of the fabrics along the edges. The use of the above-mentioned fabrics with high Walz fabric density, however, has the disadvantage of requiring very fine ballistic yarns, generally having a linear density in the range of 300 - 700 dtex, the cost of which is significantly higher than that of yarns with higher linear density.

In order to meet the most stringent ballistic protection standards, such as in the case of SK1 class bulletproof vests, it is also often necessary to stack the fabric layers in the ballistic package in a particular arrangement. For example, adjacent fabric layers are stacked on top of each other in such a way that the warp and weft yarns of one are arranged along respective directions that form an angle of 45?/-45? to the directions along which the warp and weft yarns of the other are arranged. This cross-stacking operation of the layers, however, is rather complex and increases the costs of the production process, in addition to giving rise to non-negligible quantities of textile waste.

Regardless of the type of application, an important requirement for ballistic protection articles is the ratio between the ballistic resistance characteristics and the overall weight of the article, this ratio having to be as high as possible. The ballistic resistance/weight ratio is particularly relevant in the case of ballistic protection articles intended to be worn, such as protective clothing for military and police personnel. In this case, in fact, the articles must guarantee effective protection and at the same time maximum freedom of movement for the wearer.

Furthermore, wearable ballistic protection articles must be perceived as comfortable by the wearer. The comfort property of an article can be assessed in terms of the drapability of the ballistic fabrics used, which must be as high as possible.

In consideration of the above state of the art, the Applicant has addressed the problem of providing a composite material for ballistic protection and a related preparation process that overcome the drawbacks of the prior art.

In particular, the Applicant has addressed the problem of providing a composite material in the form of a flexible sheet with which it is possible to manufacture protective articles having adequate ballistic resistance properties, relatively low weight and a reduced production cost. The composite material must also allow the preparation of wearable protective articles (e.g. bulletproof vests), which are comfortable to wear.

A further technical problem faced by the Applicant is to provide a method of preparation of the above composite material which is easy to produce and economical.

It has now been found that the above and other objects, which will be better illustrated in the following description, can be achieved by a composite material in the form of a flexible sheet and by the relative preparation process, where the composite material comprises a textile substrate comprising a warp and weft fabric formed from yarns having a relatively high linear density (denier) (greater than 800 dtex) and characterised by a relatively low Walz fabric density index (e.g. equal to or less than 25%); the fabric is mechanically reinforced by a surface coating of a polymeric binding material; the polymeric binding material has the function of binding the yarns together to form a substrate having sufficient dimensional stability to make it adequately workable during the production process of ballistic packages and related multilayer protective articles.

The fabric reinforced with the polymeric binder material has good drapeability, a characteristic that is obtained by subjecting the reinforced fabric to a mechanical softening treatment. It has also been surprisingly observed that the mechanical softening treatment also improves the ballistic resistance properties of the material.

By using yarns with a relatively high linear density, which are easier to prepare and cheaper, the composite material described here allows the manufacture of ballistic packages and related protective articles having the required level of ballistic resistance more simply and economically than with solutions known in the state of the art.

Furthermore, the preparation process is also simplified, as it is possible to achieve a certain level of ballistic protection, with the same overall weight of the multilayer package, without resorting to cross-stacking the layers of composite material.

Thanks to the above characteristics, the laminar composite material described here is suitable for producing articles for ballistic protection of various types, such as: bulletproof vests, multi-protection vests, bomb-proof suits and blankets, anti-trauma protections, panels and plates for rigid ballistic protections and armouring of vehicles and buildings, etc. In particular, the material is suitable for preparing wearable protective articles with bulletproof properties, even of protection class Ballistische Schutzwesten – SK1.

Therefore, according to a first aspect, the present invention relates to a method for preparing a composite material for ballistic protection in the form of a flexible sheet comprising:

a. preparing a woven fabric comprising weft yarns and warp yarns woven together, said weft yarns and warp yarns being ballistic yarns having a linear density equal to or greater than 800 dtex; said woven fabric having a Walz fabric density equal to or greater than 5% and less than or equal to 25%;

b. applying a polymeric binding material to at least one face of said woven fabric to bind said weft yarns and said warp yarns and obtain a reinforced woven fabric;

c. subjecting said reinforced woven fabric to a mechanical softening treatment which includes moving said reinforced woven fabric so as to cause repeated impacts of said reinforced woven fabric against a rigid impact surface.

In accordance with a second aspect, the present invention relates to a composite material for ballistic protection in the form of a flexible sheet comprising a fabric comprising weft yarns and warp yarns interwoven with each other, said weft yarns and warp yarns being ballistic yarns having a linear density equal to or greater than 800 dtex; said fabric having a Walz fabric density equal to or greater than 5% and less than or equal to 25%; said fabric being coated with at least one polymeric binding material that binds said weft yarns and said warp yarns; said composite material having a stiffness, measured according to ASTM D4032, equal to or less than 10 N.

In accordance with a third aspect, the present invention relates to a ballistic protection article comprising a plurality of superimposed layers of the composite material in the form of a flexible sheet according to the first aspect of the present invention.

The composite material according to the present invention comprises a woven fabric comprising or consisting of weft yarns and warp yarns woven together.

The warp and weft yarns are ballistic yarns. For the purposes of this description, ?ballistic yarn? means a yarn with a tenacity of at least 15 g/denier and a tensile modulus of at least 400 g/denier.

In accordance with the present invention, ballistic yarns have an effective linear density, also called yarn count, greater than 800 dtex, more preferably in the range 850 - 3400 dtex, even more preferably in the range 900 - 2500 dtex.

Examples of usable ballistic yarns are yarns based on aramid and para-aramid fibres (e.g. Twaron?, Kevlar?, Technora?, etc.), ultra-high molecular weight polyethylene (e.g. Spectra?, Dyneema?), polybenzoxazole (poly(p-phenylene-2,6,benzobisoxazole, e.g. Zylon?), liquid crystal polymers (e.g. Vectran?), glass fibres, carbon fibres and the like.

Preferably, ballistic yarns are chosen from aramid and para-aramid yarns.

Ballistic yarns are multifilament yarns; the number of filaments per yarn is not subject to any particular restrictions.

The fabric of the composite material comprises weft yarns arranged along a weft direction and warp yarns arranged along a warp direction, the warp and weft yarns being interwoven with each other to form the woven fabric.

The weave of the fabric can be chosen from those generally used for warp and weft ballistic fabrics. Preferably, the weave is chosen from: plain, twill, satin and panama (basket). Most preferably, the weave is a plain weave.

Ballistic fabric has a Walz fabric density index equal to or greater than 8% and less than or equal to 25%, preferably in the range 10% - 20%.

The density of Walz tissue, expressed as a percentage (%), is determined using the following formula:

DG (%) = (dk ds)<2>?fk?fs

Where:

dk = solid diameter (substance diameter) of the warp yarn in mm;

df = solid diameter (substance diameter) of the weft yarn in mm;

fk = number of warp yarns/cm;

fs = number of weft yarns/cm.

The solid diameter dk and/or ds of the yarn is determined by the following formula:

Where:

d represents dk or ds;

title and density represent, respectively, the title in dtex and the density in g/cm<3 >of the corresponding k or s yarn.

The above formula for determining the Walz fabric density (DG) applies to plain weave fabrics. For fabrics woven with special weaves, i.e. other than plain weave, a correction factor must be introduced into the formula. The correction factors to be used for some special weaves are given below:

The Walz fabric density of a special weave is determined by multiplying the DG density of the plain weave by the correction factor of the special weave.

In one embodiment, the number of weft yarns per cm is in the range 2 - 20/cm, preferably 4 - 10/cm.

In one embodiment, the number of warp yarns per cm is in the range 2 - 20/cm, preferably 4 - 10/cm.

The weave can be balanced, that is, have the same number of yarns/cm in the weft direction and in the warp direction, or unbalanced, with a number of yarns/cm in the weft direction different from the number of yarns/cm in the warp direction.

The yarns used can have the same linear density or different ones.

In one embodiment, the ballistic fabric has the following characteristics:

- plain weave;

- aramidic and/or para-aramid yarns having linear density in the range 850 - 3400 dtex;

- number of warp yarns per cm of weft in the range 4 - 10/cm;

- number of weft yarns per cm of warp in the range 4 - 10/cm.

Preferably, the weight of the fabric is in the range 80 g/m<2 >? 200 g/m<2>, more preferably in the range 120 g/m<2 >? 160 g/m<2>, the weight values being referred to the fabric before the application of the binding polymeric material.

The composite material according to the present invention comprises at least one polymeric binder material that binds the warp and weft yarns of the ballistic fabric. Since the ballistic fabric has a relatively low Walz fabric density, in the absence of the polymeric binder material it would be unsuitable for conventional cutting and packaging operations. The polymeric binder material is then applied to the fabric to form a reinforced fabric, i.e. to give it sufficient compactness and dimensional stability (a characteristic which is also referred to as "stiffness" hereinafter) to make it easily processable, despite the relatively low Walz fabric density, in particular avoiding excessive fraying.

Generally speaking, the binding polymer material can be chosen from among the polymer materials generally used for the production of composite materials for ballistic protection.

The binding polymer material can be either thermoplastic or thermoset.

Preferably, the polymeric binding material is a soft material, having a Tg (glass transition temperature) below -10 °C, more preferably in the range -20 °C to -50 °C.

Preferably the polymeric binding material comprises a resin selected from: polyacrylate, polyurethane, polyester, polybutadiene, polyisoprene, ethylene-propylene copolymers. The above resins can be used individually or in combination of two or more resins.

In one embodiment, the polymeric binder material comprises a mixture of at least one polyacrylate resin and at least one polyurethane resin. Preferably, the weight ratio of the polyacrylate resin to the polyurethane resin is in the range of 25:1 to 1:1, more preferably in the range of 10:1 to 3:1, the above ratios being based on the weight of the dry resins.

In general, the polymeric binder material is present in the composite material in an amount sufficient to give the fabric the desired compactness and dimensional stability. Preferably, the polymeric binder material is present in the composite material in the form of a thin, continuous surface coating. The coating may be applied to one or both faces of the fabric, with one face being more preferably the other.

Preferably, the polymeric binder material is present in the composite material in an amount by weight in the range 1 g/m<2 >? 50 g/m<2>, more preferably in the range 1 g/m<2 >? 30 g/m<2>, even more preferably in the range 2 g/m<2 >? 10 g/m<2>, said amounts by weight being referred to the weight of the dry polymeric binder material.

In one embodiment, the thickness of the coating of binder polymer material is in the range of 3-35 micrometers, more preferably in the range of 5-15 micrometers.

The polymeric binding material, in addition to the polymer resin, may include additives of the type generally used in composite materials for ballistic use such as, for example, colorants, viscosifying agents, cross-linkers, abrasive particles and the like.

The polymeric binder material may be applied to the ballistic fabric in accordance with methods known in the art for the preparation of composite materials for ballistic protection. For example, the polymeric binder material may be applied by coating, extrusion, dipping, impregnation or spraying, depending on the viscosity of the polymeric material to be applied.

In one embodiment, the polymeric binder material is applied by means of a coating technique, for example according to one or more of the following modalities: blade on cylinder, blade in air, engraved cylinder and others. The coating technique is particularly suitable, for example, for applying polymeric binder materials having a viscosity at 25 °C in the range of 1,000 - 20,000 cps, preferably 5,000 - 10,000 cps.

In another embodiment, the polymer resin may be applied in the form of a foam, said foam having, at the time of application, preferably a density in the range of 50 - 250 g/dm<3>, more preferably 150 - 200 g/dm<3>.

The process of applying the polymeric binding material may comprise, for example, the deposition of the polymeric material on at least one face of the fabric, for example by one of the techniques described above, followed by a heat treatment step of the fabric coated with the polymeric binding material to evaporate any solvents (e.g. water or organic solvents) and harden or polymerize the polymeric resin. The heat treatment may be carried out, for example, at a temperature of from 50 °C to 250 °C, more preferably from 80 °C to 200 °C. The heat treatment may be carried out, for example, in a ?rameuse? apparatus, of the type known in the state of the art.

The fabric on which the covering is applied is generally worked in the form of a ribbon and collected in reels.

In general, the fabric reinforced with the polymeric binding material has a stiffness, measured according to ASTM D4032, in the range 15 N - 35 N, preferably in the range 15 N - 25 N, more preferably in the range 15 N - 20 N, the stiffness depending on, among other factors, the characteristics of the fabric, the chemical composition of the polymeric material and the amount of polymeric material applied to the fabric.

In order to improve both the ballistic resistance properties and the drapeability, i.e., the comfort of wearable ballistic protection articles, in accordance with the present invention the reinforced fabric is subjected to a mechanical softening treatment. Such treatment comprises the action of moving the reinforced fabric to cause repeated impacts of the reinforced fabric with at least one rigid impact surface. The repeated impacts of the reinforced fabric with an impact surface reduce the stiffness of the reinforced fabric, making it softer and increasing its drapeability characteristics.

It has been surprisingly observed that the above mechanical softening treatment also significantly improves the ballistic resistance properties of the composite material, especially against non-deformable projectiles, such as steel-jacketed bullets. Presumably, the increase in the resistance to penetration by projectiles of the composite material is due to the fact that, after the mechanical softening treatment, the composite material is able to conform more easily to a projectile, enveloping it at its point of impact with the composite material. This effect is amplified in a multilayer ballistic package comprising a plurality of layers of composite material according to the present invention.

The mechanical softening treatment can be carried out, in general, using any device or process capable of causing a plurality of impacts of the reinforced fabric on a rigid impact surface. For example, the softening treatment can be carried out using the finishing processes and machines known in the state of the art generally used to improve the hand and appearance of fabrics based on non-ballistic fibres and yarns (e.g. cotton, linen, wool, etc.), such as the machines marketed under the names ENAIRGY? (Pentek), AIRO?quattro and AIRO?due (Biancalani) and others.

In one embodiment, the mechanical softening treatment comprises moving the reinforced fabric by means of an intense flow of air, which accelerates the fabric at high speed against a rigid surface against which it discharges the accumulated kinetic energy. The exclusive use of air to move the fabric prevents the fabric from rubbing against surfaces that may be abrasive or cause other surface defects. This operating principle, for example, is adopted in the AIRO? and ENAIRGY? machines (Pentek). Examples of machines that can be used to carry out the mechanical softening treatment according to the present invention are described in WO2006021978A1, IT102007901586570 and IT102010901886619.

The mechanical softening treatment can be carried out either in rope or in width, more preferably in width.

Preferably, the mechanical softening treatment is carried out at a temperature of 20 °C to 180 °C, more preferably from 20 °C to 120 °C.

The mechanical softening treatment can be carried out on the dry reinforced fabric (dry treatment) or after it has been previously wetted (wet treatment) with water or a liquid softening composition that promotes the softening of the reinforced fabric. If the mechanical treatment of the fabric is carried out in a wet state, a drying phase can be foreseen at the end of the treatment to evaporate the residual liquid present, for example at a temperature of 50 ?C to 120 ?C.

The mechanical softening treatment can be carried out continuously or discontinuously, for the time necessary to obtain the desired stiffness for the final composite material. For the purposes of this description, the stiffness of a fabric or fabric reinforced with the polymeric binding material is intended to be measured according to the ASTM D4032 standard.

Preferably, the mechanical softening treatment is continued until the stiffness of the treated composite material is equal to or less than 70% of the stiffness of the reinforced fabric before being subjected to the treatment, more preferably equal to or less than 60%.

Preferably, the stiffness of the composite material at the end of the mechanical softening treatment is in the range 5 N - 24 N, more preferably in the range 5 N - 15 N, even more preferably in the range 8 N - 12 N.

As described below, a ballistic protection article preferably comprises a plurality of superimposed layers of the composite material in the form of a flexible sheet according to the present invention. Preferably, the mechanical softening treatment is conducted on individual layers of composite material.

In accordance with the present invention, in a ballistic article the layers of composite material are advantageously held together enclosed in a fabric envelope (in English "envelope" or "cover"), without being joined together by means of adhesive resins. The envelope, which is closed by heat sealing or stitching, keeps the overlapping layers inside it and in position without modifying the drapeability of the ballistic package. Although not essential, inside the envelope the layers can still be joined together even by means of a limited number of stitching (for example from 2 to 4 stitchings of length of 5-8 cm), provided that these do not change the multilayer structure and modify its drapeability.

Preferably, a ballistic protection article comprises at least 8 layers of composite material. The minimum number of layers, however, depends on the particular type of yarn used and the level of ballistic protection desired. In general, the ballistic protection article may comprise from 8 to 100 layers of composite material, more preferably from 8 to 80 layers, even more preferably from 15 to 50 layers, even more preferably from 25 to 40 layers. The layers of composite material may be used in combination with layers of material of another composition, for example layers of reinforced fabric not subjected to the softening treatment or layers of material other than the aforementioned composite materials or reinforced fabric (e.g., rigid anti-trauma inserts).

The processes for preparing the composite material and the multilayer structure which is the object of the present invention can be carried out continuously. The products obtained are then conveniently wound into coils and marketed in this form.

The composite material in the form of a flexible sheet described here is suitable for producing articles for ballistic protection of various kinds, without particular limitations. In particular, it is suitable for being used to produce articles of ballistic protection to be worn, such as for example: bulletproof vests, multi-protection vests, suits and bomb-proof blankets. In particular, the composite material described here is suitable for preparing protective articles to be worn with bulletproof properties, even of protection class SK1.

EXAMPLES

The following examples are provided for the purpose of illustrating the present invention only and should not be construed as a limitation of the scope of protection defined by the appended claims.

EXAMPLE 1 ? Preparation of a composite material according to the present invention

A composite material according to the present invention has been prepared starting from a balanced fabric of para-aramid yarns (Twaron? type 2040, 930 dtex). The density of the Walz fabric is equal to 19.2. The fabric has a plain weave with 7.5 weft threads/cm of warp and 7.5 warp/cm of weft. The weight of the fabric, before the application of the binding polymeric material, is equal to 140 g/m<2>.

A polymeric binding material was applied to one side of the fabric by spreading with a blade in air. The polymeric binding material was formulated by mixing an aqueous dispersion of an acrylic resin (Dicrylan? AS, Tg approx. -30 ?C) and an aqueous dispersion of a polyurethane resin (Dicrylan? PHR, Tg approx. 0 ?C) in a weight ratio of acrylic resin:polyurethane resin equal to 1:4 (referred to the dry weight of the two resins).

The resulting mixture has a dynamic viscosity at 25?C equal to 6500 cps (HAAKE VISCOTESTER 2 PLUS, fixed rotor speed, rotor N?2).

The coated fabric was heated in a rameuse apparatus at a temperature of 180?C for 90 seconds.

The reinforced fabric was then wet treated (aqueous solution containing a fabric softener) in an ENAIRGY? (Pentek), with the fabric being moved around by a flow of hot air (110?C).

The final composite material had a weight of 145 g/m<2 >and a thickness of 0.30 mm.

The reinforced fabric before being subjected to the mechanical softening treatment had a stiffness measured by means of a "Pneumatic Stiffness Tester" in accordance with the ASTM D4032 standard equal to approximately 20.0 N. The stiffness of the composite material after the treatment was found to be equal to approximately 10.0 N.

EXAMPLE 2 ? Preparation of a ballistic protection article

A ballistic protection article (PB 1) was prepared by superimposing 35 layers of the composite material of Example 1 (without cross-stacking the layers). The layers of the package were enclosed within a heat-sealed fabric envelope.

The final weight of the multilayer package was 5.075 kg/m<2>.

Experimental tests have shown that the above-mentioned ballistic protection package ensures resistance to penetration by SK1 class projectiles (Technische Richtlinie Ballistische Schutzwesten (2009)).

For comparison, the same multilayer package was prepared using layers of the reinforced fabric of Example 1, which were not subjected to the mechanical softening treatment (PB 2).

The test results are reported in Table 1.

Table 1

<1 >? test with 9mm DM41 FMSJ Ruag 8.0g bullet

In the case of the comparative package PB 2, to obtain the SK1 protection level, it was necessary to form a multilayer package containing 40 layers of reinforced fabric, for a total weight of the package equal to 5.80 kg/m<2>.

From the comparison with the reference ballistic protection package PB 2 it is clear that by using the composite material PB 1 according to the present invention it is possible to obtain the desired level of protection (e.g. SK1) with a lighter and less rigid multilayer package, therefore more comfortable.

The PB 1 package according to the invention has also passed the "contact shot" test, which involves positioning the ballistic package in a contact position with the muzzle of the pressure barrel (bullet velocity equal to 410 ? 10 m/s), and the "edge shot" test, which involves firing two shots in a corner position 30 mm from the surface of the ballistic package (bullet velocity equal to 410 ? 10 m/s).

The PB 2 comparison package, on the other hand, suffered a perforation when the first shot exploded.

It should also be noted that to meet the penetration resistance requirements of class SK1 projectiles with the materials of the prior art, a ballistic package consisting of at least 36 layers of fabric is required (with cross-stacking of the layers -45?/+45?) having the following characteristics: plain weave with 11.0 weft threads/cm of warp and 11.0 warp threads/cm of weft, linear density of the yarn equal to 550 dtex, weight of the single layer of fabric equal to 126 g/m<2>, for a total weight of the package equal to 4.536 kg/m<2>. With equal performance, the relatively higher weight (approx. 11.8%) of the PB 1 ballistic package according to the invention compared to this ballistic package of the prior art is balanced by the advantages associated with the use of yarns with a higher count and the possibility of to use a simplified ballistic package preparation process, which does not require cross-stacking of the layers.

Claims (14)

1. Method for preparing a composite material for ballistic protection in the form of a flexible sheet comprising: a. preparing a woven fabric comprising weft yarns and warp yarns woven together, said weft yarns and warp yarns being ballistic yarns having a linear density equal to or greater than 800 dtex; said woven fabric having a Walz fabric density equal to or greater than 5% and less than or equal to 25%; b. applying a polymeric binding material to at least one face of said woven fabric to bind said weft yarns and said warp yarns and obtain a reinforced woven fabric; c. subjecting said reinforced woven fabric to a mechanical softening treatment which includes moving said reinforced woven fabric so as to cause repeated impacts of said reinforced woven fabric against a rigid impact surface. 2. A method according to claim 1, wherein at the end of step c the stiffness of said composite material, measured according to ASTM D4032, is equal to or less than 70% of the stiffness of the reinforced woven fabric. 3. The method of claim 1 or 2, wherein the stiffness of said composite material, measured in accordance with ASTM D4032, is in the range of 5 - 24 N. 4. A method according to any of claims 1 to 3, wherein said ballistic yarns have a linear density in the range 850 dtex - 3400 dtex, preferably in the range 900 dtex - 2500 dtex. 5. A method according to any of claims 1 to 4, wherein said number of weft yarns per cm is in the range 2 - 20/cm and, independently, said number of warp yarns per cm is in the range 2 - 20/cm. 6. A method according to any of claims 1 to 5, wherein said binding polymeric material comprises a resin selected from: polyacrylate, polyurethane, polyester, polybutadiene, polyisoprene, ethylene-propylene copolymers and combinations thereof. 7. A method according to any of claims 1 to 6, wherein said polymeric binder material comprises a mixture of at least one polyacrylate resin and at least one polyurethane resin, the weight ratio of said at least one polyacrylate resin to said at least one polyurethane resin being preferably in the range of 25:1 to 1:1, more preferably in the range of 10:1 to 3:1. 8. A method according to any of claims 1 to 7, wherein said polymeric binder material is applied in an amount by weight in the range 1 g/m<2 >? 50 g/m<2>, preferably in the range 1 g/m<2 >? 30 g/m<2>, more preferably in the range 2 g/m<2 >? 10 g/m<2>, said amounts by weight being based on the weight of the dry polymeric binder material. 9. A method according to any of claims 1 to 8, wherein said ballistic yarns comprise: aramid fibres, para-aramid fibres, ultra high molecular weight polyethylene fibres, polybenzoxazole fibres, polyester fibres, glass fibres, carbon fibres, liquid crystal polymer fibres and combinations thereof. 10. A method according to any of claims 1 to 9, wherein said reinforced woven fabric is moved by means of an air flow. 11. Composite material for ballistic protection in the form of a flexible sheet comprising a woven fabric comprising weft yarns and warp yarns woven together, said weft yarns and warp yarns being ballistic yarns having a linear density equal to or greater than 800 dtex; said woven fabric having a Walz fabric density equal to or greater than 5% and less than or equal to 25%; said woven fabric being coated with at least one polymeric binding material that binds said weft yarns and said warp yarns; said composite material having a stiffness, measured according to ASTM D4032, in the range of 5 ? 24 N. 12. A ballistic protection article comprising a plurality of superimposed layers of a composite material according to claim 1, preferably from 8 to 100 layers, more preferably from 8 to 80, still more preferably from 15 to 50 layers, still more preferably from 25 to 40 layers. 13. Article according to claim 12, wherein said layers are enclosed within a fabric casing. 14. Article according to claim 12 or 13 having a ballistic resistance of protection class SK1 according to Technische Richtlinie Ballistische Schutzwesten (2009).