WO2016169691A1

WO2016169691A1 - Structure with breathable fabric for the production of ballistic and stab-resistant protections

Info

Publication number: WO2016169691A1
Application number: PCT/EP2016/054948
Authority: WO
Inventors: Giorgio Citterio; Filippo Citterio
Original assignee: FRATELLI CITTERIO SpA
Current assignee: FRATELLI CITTERIO SpA
Priority date: 2015-04-21
Filing date: 2016-03-08
Publication date: 2016-10-27
Anticipated expiration: 2017-10-21

Abstract

The present invention relates to a structure for the realization of ballistic and anti-stab protections, including at least one textile element coupled with a polymer layer by means of process comprising a step of pressing at a temperature being determined according to the characteristics of the textile element and the polymer layer. The structure obtained with the process according to the present invention provides breathability features which makes the protections realised with the structure particularly comfortable.

Description

STRUCTURE WITH BREATHABLE FABRIC FOR THE PRODUCTION OF BALLISTIC AND STAB-RESISTANT PROTECTIONS

TECHNICAL FIELD

The present invention relates to a structure for the production of ballistic stab resistant/awl-resistant protections, in particular a structure with breathable fabric.

TECHNICAL BACKGROUND

Violent actions performed by means of cold weapons are more and more common, especially in situations in which a gun can be difficult to obtain (for example because of restrictive regulations in this matter). A cutting weapon is easily available and even simple kitchen knives can become efficacious.

Apart from everything else, the aggression by a person equipped with a blade is quicker in situations, in which the distance between the attacker and the attacked is smaller than 5 meters.

Consequently, it is necessary to have suitable protections adapted to assure stopping of cutting blows coming from a cold weapon.

The bullet-proof and/or stab resistant jackets are obtained by the superimposition of layers of fabric composed of highly resistant fibers, if necessary covered with polymeric matrices.

It is important to point out that the purely antiballistic layers are not efficacious against the blade, since the stopping mechanism of the blade is substantially different from that of the bullet.

In the bullet-proof jackets the fabric stops the bullet, since it deforms the incident bullet; actually, the deformed bullet has a larger surface and a smaller specific energy per unit of surface area and therefore it is easier to stop. On the other hand, in the stab resistant jackets, a very small part of the blade is deformed and the stopping is caused mainly by the mechanical action of the friction between the blade and highly resistant fibers and by the "barrier" action caused by the type of the surface of fabric.

The prior art stab-resistant solutions are composed of the following structures:

-Not impregnated stab-resistant densely beaten fabrics - highly covering

-Impregnated stab-resistant fabrics

-Chains of metallic materials

The densely beaten stab-resistant fabrics are described for example in the patents US6737368, US6133169, US7340779; these are fabrics obtained by means of weaving processes, in which the ratio between the dimension of the fibers and the weight of the fabric layer, known as titer, is greater than a prefixed threshold value. The Patent US8067317 describes a double protection fabric (stab- and bullet- resistant), obtained by a densifying treatment.

The Patent US7354875 describes a fabric, in which a densification of threads is obtained by mechanical processes of the finished product.

The impregnated stab-resistant fabrics, an evolution of the densely beaten stab- resistant fabrics, use polymer resins, whose function is to obtain compact fabrics without the need to use structures having high density of threads; the second solution is cheaper than the first one since the resins are cheaper than the fibers. Fabrics of this type are described for example in the Patent US8450222.

A third structure aimed at stopping the blades is the so-called chain mail; this involves metallic rings connected one to another so as to form an open structure. It is the same solution used in the Middle Ages by the horse fighters and therefore widely known. Since it is made of interlinked rings, this type of armor is not suitable for stopping awls or pointed tools if the dimension of the awls is smaller than the dimension of the chain. Another disadvantage derives from the fact that they are extremely heavy and rather uncomfortable to wear.

Each of the above described solutions has obvious disadvantages.

As it has been mentioned above, the protective jackets are formed by superimposing numerous layers of fabric kept in containing covers.

The jacket user wears it for many hours in places which can be hot and humid; thus the comfort offered by the jacket is very important and consequently very strongly felt about.

The densely beaten and impregnated fabrics present a very low breathability and consequently, they do not allow the air to circulate between the outer surface of the jacket and the clothes, thus causing strong sweating and uncomfortable situations. In addition, they are very rigid.

Attempts have been made to improve the flexibility of the bullet-proof fabrics, see for example US5124195. In this solution, the flexibility is improved by means of the production of a unidirectional textile structure having wrinkles or creases. This structure, although more flexible, does not allow any fabric breathability, since, as it has been indicated, the UD fabric is treated at a temperature and with a pressure suitable to fluidify the resin and fill all the empty spaces.

As it has been mentioned above, although they are highly permeable, the metallic meshes do not protect against pointed tools, such as ice-picks or others, since such tools insert in the rings of the mesh without finding any resistance.

OBJECT OF THE INVENTION

The main object of the present invention is to propose an element for ballistic protection and against cutting weapons, which reduces the disadvantages of the prior art solutions.

SUMMARY OF THE INVENTION

This result has been obtained, according to the present invention, by means of a structure, comprising at least one textile element including fibers having a negative axial Coefficient of Thermal Expansion (CTE), the textile element being coupled with a polymer layer by means of a process comprising a step of pressing, the polymer layer comprising at least a first resin having a positive CTE, a value of elongation at break lower than 5% and a hardness greater than 75 Shore D.

Preferably the at least first polymer resin includes one or more of the following polymers: Butyl Acrylate and Methyl Methacrylate, possibly mixed together. Optionally the at least one polymer resin includes a copolymer Butyl Acrylate - Methyl Methacrylate. In a preferred embodiment the at least one polymer resin includes 5-cloro-2-metil-2H-isotiazol-3-one and/or 2-metil-2H-isotiazol-3-one, possibly mixed together. In another embodiment, the polymer comprising butyl acrylate or methyl methacrylate also in the form of the copolymer can be cross- linked for example with the addition of isocyanates, blocked isocyanates, melamine, peroxides or the like. After the polymerization, being executed at a temperature and with a duration to be determined according to the characteristics of the cross/linking agent, the polymers or copolymers are non-melting, less exposed to attack by organic solvents and with a higher hardness compared to non-cross-linked polymers, with a further increase of the mechanical characteristics e therefore with a better resistance to penetration to spikes or sharp blades.

The structure of the present invention makes it possible to obtain a flexible and breathable bullet-proof, stab resistant and awl resistant protection, in which the presence of holes and a polymeric deposit constituted by microfractures provide at the same time breathableness, protection against blades and pointed objects,without giving up a valid protection against bullets.

According to a preferred embodiment of the present invention, the fact that the resin placed on the fiber adheres to the interface resin/fiber is not due to the chemical bonds, but results from interlacing of the matrix around the filaments composing the fiber. In a preferred embodiment of the present invention, the axial CTE of the fibers of the textile element is between -20x10^"6/°C and 0/°C, preferably in the range of - 20x10^"6 to -0,1x10^"6 per degree centigrade, while the CTE of the first resin is included between 0 and 200x10^"6/°C. In the structure according to a preferred embodiment of the present invention, the polymer layer after the treatment presents a structure with discontinuities which let air pass through. Such discontinuities can be micropores having dimensions in the range of 10 to 300 μιτι.

In an optional embodiment, the polymer layer comprises a second resin mixed with the first resin, the second resin having a hardness lower than 80 Shore A and elongation greater than 300%.

The textile element of the structure according to a preferred embodiment of the present invention comprises fibers of one of the following groups: para-aramid, co- poly-aramid, polyethylenic, etc.

According to another aspect of the present invention, a production process is provided, which facilitates the adhesion matrix/fiber; the process according to an embodiment of the present invention includes the following steps: - application of the resin to the textile element according to one of the many techniques available in the state of the art; the characteristics of the fabric and resin are those described above;

- drying the textile element with the resin joined thereto;

- pressing at a temperature T_P based on the characteristics of the used fabric and resin. The temperature is selected so as to respect the following relation:

ICTEF ^* (TP-TA)| + |CTER ^* (T_S-T_A)| > 500x 10^"6

wherein

CTE_F is the Coefficient of Thermal Expansion of the fibers of the textile element;

T_P is the pressing temperature;

T_A is the ambient temperature

CTER is the coefficient of expansion of the resin.

As indicated above, the CTE of the fabric is negative, while the CTE of the resin is positive.

The temperature Tp is preferably in the range of 20 to 200°C, the pressure is in the range of 5 to 200 bar and the pressing time is greater than 5s.

In a possible implementation of the process according to the present invention the textile element comprises polyethylene fibers, and the temperature TP is below the melting temperature of the polyethylene fibers and the polymer matrix.

The present invention makes it possible to obtain an element of ballistic protection, which is particularly effective both against bullets fired by a gun or rifle and against the attack with a cutting weapon and which at the same time has breathable characteristics. DETAILED DESCRIPTION

These and further advantages, objects and characteristics of the present invention will be better understood by those skilled in the art from the following description, with reference to the illustrative embodiments having purely illustrative character, and not intended as limiting.

A ballistic/stab-resistant protection in accordance with the present invention comprises a structure with one or more textile elements ET constituted by the intertwining of yarns composed of fibers which usually have a tensile strength greater than 8 cN/dtex, preferably greater than 18 cN/dtex, our example 20 cN/dtex, a modulus greater than 20 GPa and an elongation at break greater than 1 %.

With the term fabrics we designate: weft/warp fabrics, knitted fabrics, unidirectional fabrics, semi-unidirectional fabrics, three-dimensional fabrics, biaxial fabrics, multi- axial fabrics, felts, non-woven fabrics, continuous filament felts etc. or combinations thereof.

In accordance with a preferred embodiment of the present invention, the fibers forming the textile element ET have a negative axial Coefficient of Thermal

Expansion (CTE), preferably in the range between -20x10^"6/°C e 0.

By defining this coefficient as CTE_F, the following condition must be fulfilled:

-20X10^"6/°C < CTEF < 0/°C

The fibers of the textile element ET, in accordance with a preferred embodiment of the present invention, are partially or totally pre-impregnated with matrixes (resins) that can be of polymeric, organic or inorganic nature; in the case polymers, thermoplastic or thermosetting materials are known with plastomeric or elastomeric behavior, with liquid or solid nature, possibly with viscoelastic properties also in liquid nature.

The impregnation process of the fabric fibers include total or partial immersion treatment, coating on one or two sides, spraying, deposition by PVD, CVD, joining films, polymeric networks or web or combinations thereof.

In accordance with a preferred embodiment of the present invention, the polymer forming the positive matrix (or resin) must have a positive Coefficient of Thermal Expansion (CTE), preferably in the range between 0 and 200x10^"6/°C.

By defining this coefficient as CTE_R, the following condition must be fulfilled:

0/°C≤CTER < 200x10^"6/°C

The same fibers that form the fabrics can be partially or totally pre-impregnated with the polymers described above.

After the impregnation process the fabrics or the fibers may possibly be printed in continuous or discontinuous way. .

The manufacturing process according to a preferred embodiment of the present invention facilitates the matrix/fiber adhesion; the process includes the following steps:

- application of resin to the textile element according to one of the many techniques available in the state of the art;

optionally drying the textile element with the resin joined thereto; also this step can be performed using one of the techniques available from the state of the art;

ICTEF ^* (TP-TA)| + |CTER ^* (T_P-T_A)| > 500 x 10^"6

wherein CTE_F is the expansion (negative) Coefficient of the fibers of the textile element; T_P is the pressing temperature;

T_A is the ambient temperature;

CTER is the expansion (positive) Coefficient of the polymer resin.

For example, in one embodiment of the present invention, the following components were used:

- textile element consisting of para-aramid fibers having CTE = -2.5x10^"6/°C

- polymer comprising resin with CTE = 10x10^"6/°C

The pressing temperature used was 80°C at a room temperature of 20°C (and thus with a difference (T_P -T_A) of 60°C)

When the fabric is treated in this way unexpected breathable properties are obtained, which are caused by the presence of micro-discontinuities in the structure surface after the treatment described above: these micro-discontinuities are due to microfractures on the surface of the polymer.

To form these micro-discontinuities which let air pass through, the resin used must have very specific characteristics. In particular, the resin must be rigid with a hardness greater than 75 Shore D. In a preferred embodiment of the present invention the resin contains one or two of the following polymers: Butyl Acrylate and Methyl methacrylate. Possibly the two polymers are mixed together or can even form a copolymer Butyl Acrylate - Methyl methacrylate. In one embodiment of the present invention, Acrilem 7105 acrylic resin produced by ICAP SIRA is used. Acrilem 7105 resin contains a copolymer Butyl Acrylate - Methyl methacrylate; more specifically it includes the following components mixed together: 5-cloro-2-metil-2H- isotiazol-3-one [EC no. 247-500-7] and 2-metil-2H-isotiazol-3-one [EC no. 220-239- 6]. In another embodiment, the polymer comprising butyl acrylate or methyl methacrylate also in the form of the copolymer can be cross-linked for example with the addition of isocyanates, blocked isocyanates, melamine, peroxides or the like. After the polymerization, being executed at a temperature and with a duration to be determined according to the characteristics of the cross/linking agent, the polymers or copolymers are non-melting, less exposed to attack by organic solvents and with a higher hardness compared to non-cross-linked polymers, with a further increase of the mechanical characteristics e therefore with a better resistance to penetration to spikes or sharp blades.

It is believed that the effect of the formation of micro-discontinuities (small holes) is due to a high ratio (coefficient of cohesion/coefficient of adhesion) and a high coefficient of shrinkage.

The application of the resin is preferably carried out by means of a processing adjuvant, which is responsible for spreading the polymer onto the fabric. Typically, this consists of solvents which may or may not be water-based. In the moment in which the fabric is wetted by the resin and solvent mixture an evaporation process of the solvent and a polymer solidification process begin.

During the solidification process, the polymer tends to adhere to the fiber (adhesion) and to itself (cohesion); if the coefficient of cohesion/coefficient of adhesion ratio is above a certain value, the polymer will tend to adhere to itself and not to occupy areas where it has no support, typically at the warp and woof intersections. In these areas the polymer withdraws until it forms a hole/opening, which will then be responsible for the breathability of the fabric. The micro-cracks present on the resin that impregnates the fabric are instead due to a high coefficient of shrinkage which creates a naturally wavy surface in which the polymer islands touch each other in correspondence of their perimeters.

Not all fabrics allow the formation of holes and at the same time guarantee a good cut-awl resistant performance; it was verified that only fabrics that have a certain mass per fabric unit area/yarn count ratio facilitate these phenomena.

In particular, these are fabrics for which the ratio is between 0.09 (g/m²)dtex and 0.5

(g/m²)/dtex, preferably between 0.14 (g/m²)/dtex and 0.3 (g/m²)/dtex and more preferably of 0.15 to 0.28 (g/m²)/dtex.

In accordance with a preferred embodiment of the present invention, the textile element ET includes polyethylene fibers, in particular UHMW polyethylene fibers, such as fibers of the Dyneema® o Spectra® type. Alternatively, the textile element ET is made with para-aramid fibers, such as fibers of Kevlar®, Twaron® or Artec® and mixtures thereof.

Beaten tissue, typically with values greater than 0.5 (g/m²)/dtex do not offer spaces to the withdrawal of the matrix, and less beaten tissue, typically with values lower than 0.09 (g/m²)/dtex, allow the formation of holes, but are not effective against blades and awls because these holes become too large.

The size of the holes can vary from 10 microns up to about 300 microns, preferably from 20 to 100 microns, more preferably from 30 to 60 microns; this dimension is at most influenced by the coefficient of cohesion/coefficient of adhesion of the polymer ratio.

Optionally the resin (matrix) used in the product and in the process described above may comprise a mixture of two resins, in order to improve the anti-ballistic characteristics (bullet protection) in addition to those of the shear strength (or resistance to attack by awls).

It should be noted that the impact speed of a cutting weapon, e.g. a blade, on a protective structure is much lower than the impact speed of a bullet: typically a maximum of 10 m/s are reached by a blade attack and 200 m/s are exceeded by a bullet; the same applies to the energies involved: max 80 Joules for a blade and more than 300 Joules per a bullet.

Likewise, the bullet induces a deformation that on the cover (Trauma or Back Face Deformation) is much greater than the deformation induced by a blade.

Typically the polymers suitable to impregnate fabrics that stop bullets have low toughness, low modulus and high.

The polymer suitable to stop the blade must instead have a very high modulus, high hardness and high resistance to compression and should absorb energy with smaller deformations as compared to those induced by bullets.

Consequently, an engineered resin intended to stop a bullet may not be suitable to stop a blade.

The mixture allows to obtain several advantages:

1 The first harder, low adhesion resin is used to stop a blade with low speed load application conforming with the limited deformations that occur during this event 2.The second low-hardness, high adhesion resin with low cohesion and high elongation is instead suitable to stop the bullet as it conforms with the highest deformations typical of this ballistic event

According to a further advantage of the combination of resins, the very hard resins, such as the cut-resistant resin of the present invention, have a reduced elongation and thus tend to detach from the textile support which is rather soft and flexible. Mixing with the second resin allows the hard resin to adhere to the fiber surface in a flexible way, thus avoiding separation from the fiber surface. In this way, a further advantage of ensuring a high flexibility of the textile support while impregnating it with a hard resin can be obtained.

In detail, the stab-awl-bullet resistant resin, according to one embodiment of the present invention, is made from the mixture of two resins: one with tg > 50C° and one with tg < -30C°; the first one with hardness greater than 75 Shore D and the second one with hardness lower than 80 Shore A. preferably, the tg of the stab-awl resistant resin should be above the test temperature of the protection structure while the tg of the bullet-resistant resin should be substantially lower than the test temperature of the protection structure. The elongation at break of the cut-resistant resin is lower than 5% while the one of the bullet-resistant resin is greater than 300%.

Optionally preventive treatments may be implemented to promote mutual adhesion between the textile element ET fibers and the matrix (resin). To promote adhesion processes are known for activation of the surface of the textile element ET by washing treatments, corona treatments, plasma treatments or combination thereof, etc.

Treatments that normally follow the impregnations may provide molding at temperatures above the melting/softening temperature of the resin, in order to promote fluidization of the matrix and a better penetration of the resin in the composite.

In a particular case, when the fibers that make up the textile element ET are of polyethylene type, the penetration of the resin between the fibers is obtained through an impregnation process in which the resin/solvent solution often wets the fibers taking advantage from a low viscosity; Instead, the resin/fibers adhesion is substantially improved through a process of molding at a temperature below the melting point temperature of the resin and of the fiber. More preferably, at a temperature lower than the melting temperature of the resin but around the softening temperature of the polyethylene fiber. Precisely during the final molding operation the surface of the fiber polyethylene, while softening, adheres intimately to the resin thus improving the stab-awl-bullet resistant properties of the protective structure.

It is understood that, within the scope of the present invention, the term "polymer" refers to a polymeric material, as well as to natural or synthetic resins and their mixtures. It is also understood that the term "fiber" refers to elongated bodies, whose longitudinal dimension is much longer than the transversal dimension.

In practice, in any case, the implementation details can vary in the same way for what refers to the singular constructive elements, as described and illustrated, as well as to the nature of the indicated materials, without departing from the adopted solution concept and consequently, remaining within the protection provided by the present patent.

Claims

1 ) Structure for ballistic and anti-stab protections, comprising at least one textile element including fibers having a negative axial Coefficient of Thermal Expansion (CTE), the textile element being coupled with a polymer layer by means of process comprising a step of pressing, the polymer layer comprising at least a first resin having a positive CTE, a value of elongation at break lower than 5% and a hardness greater than 75 Shore D.

2) Structure according to claim 1 , wherein the at least one polymer resin includes a polymer Butyl Acrylate.

3) Structure according to any preceding claim, wherein the at least one polymer resin includes a polymer Methyl Methacrylate.

4) Structure according to any preceding claim, wherein the at least one polymer resin includes a copolymer Butyl Acrylate - Methyl Methacrylate.

5) Structure according to any preceding claim, wherein the at least one polymer resin includes 5-cloro-2-metil-2H-isotiazol-3-one.

6) Structure according to any preceding claim, wherein the at least one resin includes 2-metil-2H-isotiazol-3-one.

7) Structure according to claim 6, when depending on claim 5 wherein the components 5-cloro-2-metil-2H-isotiazol-3-one and 2-metil-2H-isotiazol-3-one are mixed together.

8) Structure according to any preceding claim wherein the at least one polymer resin is cross-linked with the addition of any one or more of the following: isocyanates, blocked isocyanates, melamine, peroxides.

9) Structure according to any preceding claim, wherein the CTE of the fibers of the textile element is between -20x10^"6/°C and 0/°C.

10) Structure according to any preceding claim, wherein the CTE of the at least first resin is between 0 and 200x10^"6/°C.

1 1 ) Structure according to any preceding claim, characterized in that the polymer layer after treatment presents a structure with discontinuities which allows the passage of air.

12) Structure according to claim 1 1 , wherein the discontinuities include micropores with a size between 10 and 300 μιτι.

13) Structure according to one of the preceding claims, characterized in that the polymer layer comprises a second resin mixed with the first resin, the second resin having a hardness lower than 80 Shore A and elongation greater than 300%.

14) Structure according to one of the preceding claims, characterized in that the textile element comprises fibers of one or more of the following: para-aramid, co-poli- aramid, polyethylene.

15) Structure according to any preceding claim wherein the textile element comprises fibers having a ratio between 0.15 to 0.28 (g/m²)/dtex.

16) Production process for making a structure according to any preceding claim, the process comprising the steps of:

- applying a layer of polymer in liquid form to the at least one textile element;

- drying the layer of polymer;

- pressing the structure

in which the step of pressing is carried out at a temperature of pressure T_P such that the following condition is respected:

ICTEF ^* (TP-TA)| + |CTER * (T_P-T_A)| > 500x 10^"6

wherein

CTE_F is the (negative) Coefficient of Thermal Expansion of the fibers of the textile element;

T_A is the ambient temperature CTER is the (positive) Coefficient of Thermal Expansion of the resin.

17) Production process according to claim 16 wherein the temperature T_P is between 20 and 200°C, the pressure is between 5 and 200 bar and pressing time is longer than 5s.

18) Production process according to claim 16 or 17 wherein the textile element comprises polyethylene fibers and the temperature T_P is lower than the melting temperature of the polyethylene fibers and of the polymer layer.

19) Ballistic protective article comprising a structure according to any claim 1 to 15.