WO2012004392A1

WO2012004392A1 - Ballistic resistant article

Info

Publication number: WO2012004392A1
Application number: PCT/EP2011/061660
Authority: WO
Inventors: Martin Antonius Van Es; Harm Van Der Werff
Original assignee: Dsm Ip Assets B.V.
Priority date: 2010-07-08
Filing date: 2011-07-08
Publication date: 2012-01-12

Abstract

The invention relates to a ballistic resistant article comprising a strike face component containing a rigid panel comprising fibers wherein said article further comprises a pliable back face component containing fibers.

Description

BALLISTIC RESISTANT ARTICLE

The invention relates to a ballistic resistant article comprising a strike face component containing a rigid panel comprising fibers. The invention further relates to various products containing said article and to a method for life protection.

A ballistic resistant article is an item that offers protection to its user by resisting an impact from for example gun-fired projectiles, shrapnel and fragments fired at the user. Rigid panels, also commonly referred to in the art as ballistic panels, are widely used in the construction of such articles. In turn, ballistic resistant articles find extensive use in automotive armour industry, ballistic resistant garments e.g. vests, helmets, as well as architectural applications e.g. bank counters, safe rooms, and guard stations, to name a few.

EP 0 833 742 discloses for example a ballistic resistant article containing rigid panel comprising a compressed stack of monolayers, each monolayer containing unidirectionally reinforcing fibers and a plastic matrix material. The stack of monolayers was compressed to at least 98.0% of its theoretical maximum density. Such an article has very good ballistic resistance; however, it was observed that its ballistic resistance can be further improved.

EP 1 627 719 discloses a multilayered ballistic resistant article comprising unidirectional monolayers of ultra high molecular weight polyethylene (UHMWPE). A panel of 20.85 kg/m2 was made by compressing a stack of such UHMWPE monolayers at about 120°C and 140 bar for about 1 hour. The antiballistic properties of the multilayered article were determined in example 5 whereby a backing comprising 30 layers of aramid fibers was laid on the multilayered article, without any bonding materials. Areal density of the layers of aramid fibers is not disclosed. The backing and the multilayered article were positioned in a fabric pocket together with a 102 mm clay backing. Upon shooting with M-80 bullets the average trauma proved to be 12.5mm at an average velocity of 853 m/s.

WO91/00490 discloses composite ballistic resistant articles comprising at least one hard rigid layer and one fibrous layer; the composite ballistic resistant articles having a mass efficiency equal to or greater than about 2.5. Mass efficiency is defined as the areal density of armor steel grade required to defeat a threat devided by the areal density of composite ballistic resistant article required to defeat the threat. The hard rigid layer may comprise e.g. metals and hard ceramics. The fibrous layer may comprise several kinds of fibers including glass fibers, aramid fibers and high molecular weight polyethylene fibers and is formed by moulding the fibers and matrix mateial under heat and pressure. In example 1 a panel with an areal density of 121 kg/m2, comprising titanium diboride ceramic tiles and a laminated composite panel, was tested against projectiles with a speed of 935 m/s. The mass efficiency in comparison with a roll-hardened armor plate was disclosed to be 3.3. The fibrous layer had an areal density of 24 kg/m2 and comprised polyethylene fibers that were compressed at 124°C and 2,9MPa for 40 minutes. One aim of the present invention may thus be to provide a ballistic resistant article having good ballistic properties.

The invention provides a ballistic resistant article comprising a strike face component containing a rigid panel comprising fibers wherein said article further comprises a pliable back face component containing fibers.

It was observed that by adding a pliable back face component to an article comprising a rigid panel as strike face, the strike face and the back face components may synergistically interact with each other to improve various properties of said article. In particular it was observed that the article of the invention may exhibit an improved ballistic resistance over known ballistic resistant articles such as those of EP 0 833 742. For simplicity, the article of the invention is also referred to herein as the inventive article.

It was also observed that the inventive article may show an increased V₅₀. By V₅₀ is herein understood the velocity of a 9 mm x 19 mm FMJ Parabellum bullet at which 50 % of the shots penetrate said article and 50 % of the shots are stopped by said article.

The strike face component and the back face component of the inventive article comprise fibers. By "fiber" is herein understood an elongated object the length dimension of which is much greater than its transverse dimensions of width and thickness. The term fiber also comprises the embodiments of a monofilament, a multifilament, a ribbon, a strip, a tape and a film. The fibers may have a continuous or a discontinuous length with a regular or an irregular cross-section. In a preferred embodiment, the fiber has a tape-like shape, such a fiber being referred to herein simply as tape. Typically the tape has a width of 1600mm or less. The tape has preferably a width of between 1 mm and 500 mm, more preferably between 2 mm and 200 mm, even more preferably between 5 mm and 150 mm, most preferably between 10 mm and 120 mm. The tape has preferably a thickness of between 10 μηη and 200 μηι, more preferably between 25 μηη and 100 μηη, most preferably between 30 μηη and 60 μηι.

The fibers used in accordance with the invention may be inorganic fibers or polymeric fibers. However, the preferred fibers utilized in the present invention are polymeric fibers, in particular in view of their high strength and low weight.

Examples of suitable inorganic fibers include glass fibers, e.g. S-2 or E glass fibers, glass basalt fibers, basalt fibers, ceramic fibers and carbon fibers. By "polymeric fiber" is herein understood a fiber made of a polymer suitable to be formed into a fiber.

Preferred polymers include but are not limited to polyamides and polyaramides, e.g. poly(p-phenylene terephthalamide) (known as Kevlar®); poly(tetrafluoroethylene) (PTFE); poly{2,6-diimidazo-[4,5b-4',5'e]pyridinylene-1 ,4(2,5-dihydroxy)phenylene} (known as M5); poly(p-phenylene-2, 6-benzobisoxazole) (PBO) (known as Zylon®); poly(hexamethyleneadipamide) (known as nylon 6,6), poly(4-aminobutyric acid) (known as nylon 6); polyesters, e.g. poly(ethylene terephthalate), poly(butylene terephthalate), and poly(1 ,4 cyclohexylidene dimethylene terephthalate); polyvinyl alcohols;

thermotropic liquid crystal polymers (LCP) as known from e.g. US 4,384,016; but also polyolefins e.g. homopolymers and copolymers of polyethylene and/or polypropylene.

A particularly preferred material for manufacturing the polymeric fibers is polyolefin, in particular polyethylene, more preferably ultrahigh molecular weight polyethylene (UHMWPE), i.e. a polyethylene having an intrinsic viscosity (IV) of at least 5 dl/g, preferably of at least 10 dl/g. By using such fibers an improved ballistic inventive article is obtained.

Preferably, the UHMWPE utilized to make fibers suitable for the present invention is a linear polyethylene, i.e. a polyethylene with less than one side chain or branch per 100 carbon atoms, and preferably less than one side chain per 300 carbon atoms, a branch generally containing at most 10 carbon atoms. The UHMWPE may further contain up to 5 mol% of alkenes that may or may not be copolymerized with it, such as propylene, butene, pentene, 4-methylpentene or octene. The UHMWPE may further contain additives that are customary for UHMWPE fibers, such as anti- oxidants, thermal stabilizers, colorants, etc., preferably up to 15 % w/w of the total weight of the UHMWPE plus the additives, preferably 1 -10 % w/w of the total weight of the UHMWPE plus the additives. The UHMWPE may further contain a polyethylene with lower molecular weight, preferably up to 10 % mol of the total weight of the UHMWPE plus the polyethylene with lower molecular weight. UHMWPE fibers and methods for manufacturing thereof have been described in various publications, including EP 0 205 960 A, EP 0213208 A1 ,

US 4 413 1 10, WO 01 73173 A1 , and Advanced Fiber Spinning Technology,

Ed. T. Nakajima, Woodhead Publ. Ltd (1994), ISBN 1 -855-73182-7, and references cited therein, all incorporated herein by reference. In these publications, UHMWPE fibers are made by a gel spinning process and have favorable mechanical properties, e.g. a high modulus and a high tensile strength.

In a preferred embodiment of the invention, the fibers are tapes and/or films, in particular polymeric tapes and/or films made from the above mentioned polymers. Such polymeric tapes and/or films might be produced by feeding the polymer to an extruder, extruding a tape or a film at a temperature above the melting point thereof and drawing the extruded polymeric tape or film. If desired, prior to feeding the polymer to the extruder, the polymer may be mixed with a suitable liquid organic compound, for instance to form a gel, such as is preferably the case when using UHMWPE.

A preferred process for the formation of such polymeric films or tapes in case UHMWPE is used for the manufacturing thereof comprises agglomeration of an UHMWPE powder into a film or tape, followed by drawing. It is for example possible to feed the UHMWPE powder between a combination of endless belts, compression- moulding the polymeric powder at a temperature below the melting point thereof and rolling the resultant compression-moulded polymer followed by drawing. Such a process is for instance described in US 5,031 ,133, which is incorporated herein by reference. It is preferred that the UHMWPE is drawable in the solid state, e.g. as described in US 5,773,547. Drawing of the produced tapes or films may be carried out by means known in the art.

The fibers and in particular the polymeric fibers utilized in accordance with the invention, preferably have a tensile strength of at least 0.3 GPa, more preferably at least 1 GPa, most preferably at least 1 .5 GPa. In a preferred embodiment, the fibers are UHMWPE fibers having a tensile strength of at least 1 GPa, more preferably at least 1 .5 GPa. The fibers and in particular the polymeric fibers utilized in accordance with the invention, preferably have a tensile modulus is preferably at least 30 GPa, more preferably at least 50 GPa, most preferably at least 60 GPa. The manufacturing of fibers and in particular of polymeric fibers having such high tensile strengths and modulus are known in the art, examples of processes for making thereof being given hereinabove. By "strike face component" is herein understood the component of the ballistic resistant article positioned to receive a ballistic impact, e.g. the impact of a bullet, prior to the back-face component. The strike face component is positioned between the threat and the thing or body to be protected by the threat.

By "rigid panel" is herein understood a rigid, i.e. non-pliable, panel comprising an assembly of fibers and optionally a binder. A binder is mostly used when the fibers forming said assembly of fibers are inorganic fibers and is preferably a thermoplastic or a thermosetting polymer, more preferably said binder being chosen from the group consisting of epoxy resins, polypropylene, vinylester , polybutylene terephthalate, phenolic resins and polyurethane. Suitable examples of binders are described in e.g. EP 0191306 B1 , EP 1 170925 A1 , EP 0683374 B1 and

EP 1 144740 A1 .

By "rigid" or "non-pliable" panel is herein understood a panel which

25 when havinq a width of about 100 mm it presents a deflection of at most mm at

[AD] the point of load under a weight of 1 kg where the weight is applied 100 mm from a support point of the panel, when said panel is subjected to a drape test. With [AD] is herein meat the areal density of the panel expressed in kg/m². Preferably, the panel

15

has a deflection of at most mm when measured under the above conditions,

[AD]

5

more preferably a deflection of at most mm.

[AD]

If a weight of e.g. 1 kg would not be available or practically difficult to apply, "rigid" or "non-pliable" for a panel can be determined by the following alternative test, hereinafter referred to as 'shortened-drape-test': have the panel unsupported at one side, e.g. by protruding it from a table edge, for 300 mm and check the downward deflection under its own weight. If the deflection is less then 10 mm the panel is referred to as rigid, otherwise the panel is referred to as pliable.

In an embodiment of the invention, the assembly of fibers used to prepare the panel comprises randomly arranged chopped or staple fibers, i.e. fibers having discontinuous lengths. Preferably, the fibers in said assembly are polymeric fibers. In another embodiment, said assembly of fibers comprises fabrics, preferably woven fabrics, containing fibers. In yet another embodiment, said assembly of fibers comprises unidirectionally oriented fibers, i.e. fibers running along a common direction in a plane.

A rigid panel suitable for the present invention can be manufactured according to well-known methods in the art. In a preferred embodiment, the rigid panel is obtained by compressing under temperature and pressure an assembly of polymeric fibers, such a panel being also referred to as a compressed rigid panel. The fibers may suitably be supplied in the form of sheets.

In another embodiment of the invention, the fibers are polymeric fibers and the assembly of polymeric fibers which is used to prepare the rigid panel comprises a plurality of fabric layers, said fabric layers comprising polymeric fibers. Preferably, the fabric layers have a woven structure. Preferably, the woven structure is chosen from the group consisting of a plain weave, a satin weave, a twill weave and a crow-foot weave.

In a preferred embodiment however, the rigid panel is prepared by stacking and compressing two or more sheets comprising monolayers of polymeric fibers, preferably monolayers comprising a fabric made of polymeric fibers, more preferably monolayers containing unidirectionally aligned polymeric fibers. The monolayers may also contain a binder. The purpose of the binder may be to hold said fibers in place in order to improve the ease of operation of the monolayers or sheets comprising thereof. As already mentioned hereinabove, suitable binders are described in e.g. EP 0191306 B1 , EP 1 170925 A1 , EP 0683374 B1 and EP 1 144740 A1 . It was observed that good to very good results were obtained when neither the monolayers, nor the sheets, nor the rigid panel of this embodiment comprise a binder or any other material the purpose of which being to hold the fibers together.

By a monolayers containing unidirectionally aligned fibers is herein understood that a majority of the fibers in the monolayer, e.g. at least 70 mass% of the total mass of fiber in said monolayer, more preferably at least 90 mass%, most preferably about 100 mass%, run along a common direction. Preferably, the fiber direction in a monolayer is at an angle a to the fiber direction in an adjacent monolayer, whereby a is preferably between 5 and 90°, more preferably between 45 and 90° and most preferably between 75 and 90°.

To compress an assembly of polymeric fibers, and more in particular an assembly containing a stack of two or more sheets, said assembly or stack is generally placed in an open mould. The open mould may also have a female part and a male part. The assembly or stack may also be clamped to one part of the mould, generally to the female part. To obtain a flat panel, both the male and the female parts of the mould should be planar; whereas to obtain a three dimensionally shaped panel, said male and female parts may contain curvatures or other shaped geometries in one or more directions. After placing the assembly or said stack of sheets in the mould, the mould is closed and pressure is applied on said assembly or stack. In order to compress the assembly or stack under temperature, the mould is heated. During the compression under temperature, the assembly or stack is consolidated into a rigid panel.

The temperature during compression is generally controlled through the mould temperature. The temperature during the compression step is preferably chosen below the melting temperature of the polymeric fibers as measured by DSC. If DSC cannot determine the melting temperature of a polymeric fiber then by said melting temperature is understood herein the temperature at which the polymeric fibers start to lose their mechanical properties, e.g. when in a temperature interval of 5°C the tensile strength of the fibers decreases with more than 5% of the tensile strength of the fiber as measured at room temperature. In case the assembly of polymeric fibers used to manufacture the panel contains more than one type of polymeric fibers, by melting temperature is herein understood the lowest melting temperature of the polymeric fibers.

Preferably the temperature during the compression step is at least 5

°C, preferably at least 10 °C and even more at least 20 °C below the melting temperature of the polymeric fiber. For example, in the case of polyethylene and more particular of UHMWPE fibers, often having a melting temperature of about 155 °C, a mould temperature of preferably below 145 °C, more preferably below 135 °C will be chosen. The minimum temperature generally is chosen such that a reasonable speed of consolidation is obtained. In this respect 50 °C is a suitable lower temperature limit, preferably this lower limit is at least 75 °C, more preferably at least 95 °C, most preferably at least 1 15 °C.

The pressure during consolidating preferably is at least 5 bars, more preferably at least 50 bars, even more preferably at least 100 bars and most preferably at least 250 bars. Good results were obtained when the assembly of polymeric fibers was compressed at pressures of at least 350 bars, preferably of at least 450 bars. In this way a better anti-ballistic performance is achieved. Optionally, the compression may be preceded by a lower pressure pre-compressing step. Pressure during this pre-compressing step may vary between 1 bar and 5 bars. After pre-compressing and before consolidating the mould may be opened and the occurrence of blisters may be verified, which may be removed by e.g. piercing with a sharp object. Other options to prevent blisters include degassing during molding or use of vacuum. The optimum time for consolidation generally ranges from 5 to 120 minutes and can be verified through routine experimentation.

In another embodiment of the invention, the rigid panel is made by pultrusion. Preferably, the fibers used in making pultruded panels are inorganic fibers. Pultrusion is a process of manufacturing of rigid panels containing an assembly of fibers whereby fibers are pulled through a binder, e.g. a thermosetting or thermoplastic polymer, optionally followed by a separate preforming step. When a thermosetting polymer is used as binder, the pultruded panel is introduced into a heated die where said polymer undergoes polymerization, subsequently followed by cooling the panel to form a rigid panel. Many thermosetting polymer types may be used in pultrusion including polyester, polyurethane, vinylester and epoxy. When a thermoplastic polymer is used as the binder, e.g. polybutylene terephthalate (PBT), the panel is made by either impregnating the assembly of fibers or surrounding said assembly with a sheet of the thermoplastic polymer which is then molten up. Consolidation of the panel into a rigid panel may be performed by cooling the panel after melting of the thermoplastic polymer. In case the panel is also compressed, preferably cooling is performed while maintaining pressure.

The rigid panel can have different shapes, e.g. planar or curved in one or more directions, and different shape-forms e.g. rectangular, square or circular. Preferably the rigid panel has a planar shape with a shape-form adapted for the application for which the inventive article is intended.

In a preferred embodiment of the invention, the rigid panel contains a compressed stack of monolayers, each monolayer containing unidirectionally aligned fibers, preferably UHMWPE fibers, more preferably UHMWPE tapes, and optionally a binder in at most 20 wt% of the total weight of the monolayer, the fiber direction in each monolayer being rotated with respect to the fiber direction in an adjacent monolayer, the monolayers having a fiber weight of preferably between 25 and 150 gr/m², and wherein the compressed stack of monolayers has an experimental density (PEXP) of at least 90.0%, preferably of at least 95.0%, more preferably of at least 98.0% of the theoretical maximum density. The theoretical density is the sum of (weight fraction of a constituent [e.g. fiber, binder] times its specific density) for all individual constituents of said panel. Such a rigid panel can be obtained in accordance with EP 0 833 742, the disclosure of which being herein incorporated by reference. The experimental density can be measured by accurate weighing and measurement of the volume of said panel using a Vernier calliper. The standard deviation according to this density measurement is 0.002-0.004 g/cm³.

The areal density (AD) of the rigid panel used in accordance with the invention may vary within wide limits and is preferably chosen in relation to the threat against which the article of the invention is used. Preferably, for example for a

9 mm x 19 mm FMJ Parabellum bullet, the AD of the panel is at least 1 kg/m², more preferably at least 3 kg/m², most preferably at least 5 kg/m². Although only limited by the application for which the inventive article is intended, said AD is preferably at most 500 kg/m², more preferably at most 300 kg/m², most preferably at most 100 kg/m². In a preferred embodiment, the AD of the strike face component is substantially the same with the AD of the panel contained by said strike face. By substantially the same is herein understood that the difference between the AD of the strike face component and the AD of the rigid panel contained by said strike face component is at most 10%, more preferably at most 5%, most preferably at most 1 %.

By "back face component" is herein understood the component of inventive article, positioned toward an object, thing or body which is to be protected by said article from a ballistic impact. The back face component is positioned between the strike face component and said object, thing or body.

By "pliable back face component" is herein understood a back face component which when having a width of about 100 mm it presents a deflection of at

100

least W^{* mm a}* *^ne point of load under a weight of W kg where the weight is

applied 100 mm from a support point of the back face component, when said component is subjected to a drape test. Where W is chosen such that D< 0,03 m. The drape test is illustrated in figure 1 . With [AD] is herein the areal density of the back face component expressed in kg/m². Preferably, the back face component has a

200

deflection ratio D of at least W^* mm when measured under the above conditions,

[AD]

300

more preferably a deflection of at least W^* mm.

[AD]

In a preferred embodiment, the strike face and the back face components of the inventive article are designed or shaped in such a way so as to overlap with each other over a substantial part of their surfaces, more preferably to fully overlap each other. Overlap with each other over a substantial part of their surfaces means that a projection of the strike face on a third surface parallel to the strike face and the projection of the back face on that third surface substantially coincide.

The polymeric fibers contained by the back face component may be the same with or different than the fibers contained by the strike face component of the inventive article. Preferably, said both components contain polymeric fibers

manufactured from the same polymer although said fibers may have different mechanical properties. More preferably, the same polymeric fibers are used in manufacturing both said components.

In a preferred embodiment the strike face component of the inventive article comprises unidirectional aligned polyethylene fibers, more preferably

unidirectional aligned ultra high molecular weight polyethylene fibers, and the back face component comprises polyethylene fibers, more preferably ultra high molecular weight polyethylene fibers. Preferably the areal density of the back face component, AD_BF is between 10% and 90 %, more preferably between 20% and 80 %, most preferably between 40% and 60 % of the areal density of the inventive article.

In another preferred embodiment the strike face component of the inventive article comprises woven polyethylene fibers, more preferably ultra high molecular weight polyethylene fibers, the fibers in the strike face component preferably having a tape-like shape, and the back face component comprises polyethylene fibers, more preferably ultra high molecular weight polyethylene fibers. Preferably the areal density of the back face component, AD_BF is between 10% and 90 %, more preferably between 20% and 80 %, most preferably between 40% and 60 % of the areal density of the inventive article.

In another preferred embodiment the strike face component of the inventive article comprises unidirectional aligned polyethylene fibers, more preferably unidirectional aligned ultra high molecular weight polyethylene fibers, and the back face component comprises aramid fibers. Preferably the areal density of the back face component, AD_BF is between 10% and 90 %, more preferably between 20% and 80 %, most preferably between 40% and 60 % of the areal density of the inventive article.

In another preferred embodiment the strike face component of the inventive article comprises unidirectional aligned aramid fibers, and the back face component comprises aramid fibers. Preferably the areal density of the back face component, AD_BF is between 10% and 90 %, more preferably between 20% and 80 %, most preferably between 40% and 60 % of the areal density of the inventive article. In another preferred embodiment the strike face component of the inventive article comprises aramid fibers, and the back face component comprises unidirectional aligned polyethylene fibers, more preferably unidirectional aligned ultra high molecular weight polyethylene fibers. Preferably the areal density of the back face component, AD_BF is between 1 0% and 90 %, more preferably between 20% and 80 % , most preferably between 40% and 60 % of the areal density of the inventive article.

Preferably the back face component contains at least one sheet comprising polymeric fibers. More preferably, said back face component contains at least 2 sheets, more preferably at least 4 sheets. Each sheet forming the back face component preferably comprises at least one monolayer, more preferably it comprises a plurality of monolayers. By plurality of monolayers is herein understood that the sheet comprises at least 2 monolayers, more preferably at least 4 monolayers. Preferably, the monolayers contain unidirectionally aligned fibers and optionally a binder, although it is preferred that the monolayers are free of a binder. Preferably the direction of alignment of fibers in a monolayer is at an angle a with the direction of alignment of fiber in an adjacent monolayer. Preferred angles a, are those detailed hereinabove in relation to the monolayers used to manufacture the panel utilized according to the invention.

In a preferred embodiment of the monolayers forming the sheets contained by the back face component, the polymeric fibers utilized in manufacturing thereof form a woven structure. Preferably, the woven structure is chosen from the group consisting of a plain weave, a satin weave, a twill weave and a crow-foot weave. Most preferred is a plain weave. When woven monolayers are used, preferably the polymeric fibers have the tape embodiment as detailed hereinabove, i.e. the fibers having a tape-like shape.

The sheets forming the back face component are preferably unconnected to each other, i.e. they are substantially free of connecting means as for example glue spots, stitches, welding spots and the like. However, to improve handle- ability, said sheets may be connected to each other preferably at their periphery such that the connected area is preferably at most 1 0% of the total area of the sheets, more preferably at most 5%, most preferably at most 3%. Such construction ensures the pliability of the back face component.

The pliability of the back face component depends largely on the number and areal density of the sheets forming thereof, the number of monolayers forming a sheet and the amount of connection places between the different sheets. By increasing the number and/or the areal density of said sheets, e.g. by using more monolayers to construct thereof, the pliability of sheets and consequently the pliability of the back face component will decrease. Doing the opposite, the pliability of the back face component will increase.

In a preferred embodiment, the areal density of the back face component (AD_BF) and the areal density of the strike face component (AD_SF) fulfil the following relationship:

0.05xAD_BF < ADSF < 19xAD_BF

more preferably the following relationship:

0.25xAD_BF < ADSF < 3xAD_BF

even more preferably the following relationship

0.5xAD_BF < ADSF < 2xAD_BF

most preferably:

wherein by "=" is herein meant substantially the same.

In a more preferred embodiment, AD_BF is at least 10% of the areal density of the inventive article while preferably the AD_SF is at most 90% of the areal density of the inventive article.

In an even more preferred embodiment, AD_BF is at least 20% of the areal density of the inventive article while preferably the AD_SF is at most 80% of the areal density of the inventive article.

In an even more preferred embodiment, AD_BF is at least 40% of the areal density of the inventive article while preferably the AD_SF is at most 60% of the areal density of the inventive article.

In an even more preferred embodiment, AD_BF is between 10% and

90 %, more preferably between 20% and 80 %, most preferably between 40% and 60 % of the areal density of the inventive article while preferably the AD_SF is the remaining percentage, i.e. up to 100%, of the areal density of the inventive article.

It was observed that for the above ranges of areal densities specific to the strike face and to the back face components, the synergistic cooperation of said two components was enhanced.

In a further preferred embodiment, the inventive article consists of a strike face component as detailed hereinabove and a back face component as detailed hereinabove. The present invention also relates to a device comprising an assembly of parts, wherein at least one part contains the inventive article. By "device" is herein understood an article for example a piece of equipment, e.g. vehicle, boat, aircraft; or a mechanism, e.g. door, spare part of a machine or of a piece of an equipment designed to serve a special purpose or perform a special function and can consist of more than one articles (multi-article assembly).

In a special embodiment of the device of the invention, said device comprises a sheet of glass, wood, carbon and/or metal or combinations thereof, wherein the inventive article is attached thereto and positioned behind said sheet.

The present invention further relates to anti-ballistic vests, helmets, garments, blankets, shields, comprising the inventive article.

The present invention further relates to a product for automotive applications (car parts, etc.), marine applications (ships, boats, panels, etc.), aerospace applications (planes, helicopters, panels, etc.), defence/life-protection applications (ballistic protection, body armour, ballistic vests, shields, ballistic helmets, ballistic vehicle protection, etc.), architectural applications (windows, doors, (pseudo-)walls, shields, etc.), wherein said product contains the inventive article.

In yet another embodiment, the present invention provides for a ballistic resistant article according to the invention, for life protection applications, wherein the ballistic resistant article exhibits a V₅₀ equal to or higher than 460 m/s, measured according to Stanag 2920 using 9 mm x 19 mm FMJ Parabellum bullets.

In another aspect, the present invention provides for a method for life protection, wherein the ballistic resistant article or the device disclosed herein, is positioned between a life-threat e.g. a projectile, explosive fragment, and a human, or an animal, or a human and an animal, in such a way to cover in full at least vital parts of the body of the human, or of the body of the animal, or the bodies of the human and the animal.

For example, in case in which the ballistic resistant article of the present invention is a portable or fixed wall comprising one or more compressed panels in such a way that the surface of the wall facing the incoming life-threat is covered in full by one or more compressed panels, and this wall is positioned between a human, or an animal, or a human and an animal, in such a way to cover partly or in full vital parts of the body of the human, or the body of the animal, or the bodies of the human and the animal, then this portable or fixed wall can protect the life of the human or the animal or the lives of the human and the animal, who position themselves behind this wall.

Test methods for various parameters referred to herein, are as follows:

· Intrinsic Viscosity (IV) of UHMWPE is determined according to method PTC- 179 (Hercules Inc. Rev. Apr. 29, 1982), or alternatively according to ASTM D1601 , at 135°C in decalin, the dissolution time being 16 hours, with DBPC as anti-oxidant in an amount of 2 g/l solution, by extrapolating the viscosity as measured at different concentrations to zero concentration;

· Tensile strength of fibers is defined and determined on multifilament yarns as specified in ASTM D885M, using a nominal gauge length of the fiber of 500 mm, a crosshead speed of 50%/min and Instron 2714 clamps, of type Fiber Grip D5618C. For calculation of the strength, the tensile forces measured are divided by the titer, as determined by weighing 10 meters of fiber; values in GPa for are calculated assuming the natural density of the polymer, e.g. for UHMWPE is 0.97 g/cm³.

The tensile properties of tapes: tensile strength and tensile modulus are defined and determined at 25 °C on tapes of a width of 2 mm as specified in ASTM D882, using a nominal gauge length of the tape of 440 mm, a crosshead speed of 50 mm/min.

• The melting temperature (also referred to as melting point) of a polymer is

determined by DSC on a power-compensation PerkinElmer DSC-7 instrument which is calibrated with indium and tin with a heating rate of 10°C/min. For calibration (two point temperature calibration) of the DSC-7 instrument about 5 mg of indium and about 5 mg of tin are used, both weighed in at least two decimal places. Indium is used for both temperature and heat flow calibration; tin is used for temperature calibration only.

• The experimental V₅₀ value was measured according to Stanag 2920 using 9 mm x 19 mm FMJ Parabellum bullets and was obtained from the average speeds of the three highest speeds at which a stop occurred and the three lowest speeds at which a perforation occurred. In case only two stops or only two perforations are obtained, V₅₀ is obtained from the two highest stops and two lowest perforations. The present invention will now be illustrated by way of the following examples and comparative experiments without however being limited thereto.

EXAMPLES

Materials

Dyneema® HB26, a unidirectional sheet material made of UHMWPE fibers with a melting temperature of 155 °C, decomposition temperature higher than 300 °C, density 0.95- 0.98 Kg/m³, areal density 257-271 g/m², was used to prepare ballistic resistant articles according to the invention and also for comparative experiments.

Rigid panels were prepared by compressing 0.2 m x 0.2 m HB26 sheets at 130°C and under a pressure of 70 bars. The areal density of each of the panels thus prepared depended on the number of HB26 sheets used to construct thereof.

The pliable component was prepared by assembling a number of

HB26 sheets to yield a component having the desired AD. The sheets were not connected over their surface but only at their corners to ease their manipulation.

Example 1

The strike face consisted of a rigid panel made by compressing three

HB26 sheets and had an AD of about 0.8 kg/m².

The pliable component consisted of nine HB26 sheets and had an AD of about 2.4 kg/m². Said pliable component had a deflection of more than 20 mm when subjected to a load of 0,1 kg. (W^*100/AD = 4,2 ) measured according to the drape test presented hereinabove. According to the shortened-drape test, the rigid panel

(measured at 40^*40 cm panels) had a downward deflection of less than 2mm, the pliable component had a downward deflection of more than 100mm.

Example 2

The strike face consisted of a rigid panel made by compressing six

HB26 sheets and had an AD of about 1 .6 kg/m².

The pliable component consisted of six HB26 sheets and had an AD of about 1 .6 kg/m². Said pliable component had a deflection of more than 15 mm when subjected to a load of 0,05 kg. (W^*100/AD = 3,1 ) measured according to the drape test presented hereinabove. According to the shortened-drape test, the rigid panel (measured at 40^*40 cm panels) had a downward deflection of less than 2 mm, the pliable component had a downward deflection of more than 100 mm.

Example 3

The strike face consisted of a rigid panel made by compressing nine

HB26 sheets and had an AD of about 2.4 kg/m².

The pliable component consisted of three HB26 sheets and had an AD of about 0.8 kg/m². Said pliable component had a deflection of more than 15 mm when subjected to a load of 0,025 kg. (W^*100/AD = 3,1 ) measured according to the drape test presented hereinabove. According to the shortened-drape test, the rigid panel (measured at 40^*40 cm panels) had a downward deflection of less than 2mm, the pliable component had a downward deflection of more than 100mm.

Comparative Experiment 1

The strike face consisted of a rigid panel made by compressing twelve HB26 sheets and having an AD of about 3.2 kg/m². According to the shortened- drape test, the rigid panel (measured at 40^*40 cm panels) had a downward deflection of less than 2mm. There was no pliable component. Comparative Experiment 2

The strike face consisted of a pliable component consisting of twelve HB26 sheets and having an AD of about 3.2 kg/m². Said pliable component had a deflection of more than 15 mm when subjected to a load of 0,1 kg. (W^*100/AD = 3, 1 ) measured according to the drape test presented hereinabove. According to the shortened-drape test the pliable component (measured at 40^*40 cm panels) had a downward deflection of more than 100mm.

No rigid panel was used in the article of this comparative experiment.

The results of the above comparative experiments and examples are presented in Table 1 . Table 1

As can be seen from Table 1 , a ballistic resistant article comprising a rigid panel as the strike face component and a pliable back face component may present increased V₅₀ over ballistic articles that did not comprise both components. It can also be seen that the two components synergistically interact to provide a V₅₀ that is always higher than a theoretical one calculated by applying the rule of mixtures.

Claims

A ballistic resistant article comprising a strike face component containing a rigid panel comprising fibers wherein said article further comprises a pliable back face component containing fibers, wherein the areal density of the back face component (AD_BF) and the areal density of the strike face component (AD_SF) fulfil the relationship 0.05xAD_BF < AD_SF < 19xAD_BF.

The article of claim 1 wherein the fibers have a tape-like shape.

The article of any one of the preceding claims wherein the fibers are made of a polymer chosen out of the group consisting of polyamides, polyaramides, poly(p-phenylene terephthalamide), poly(tetrafluoroethylene) (PTFE), poly{2,6-diimidazo-[4,5b-4',5'e]pyridinylene-1 ,4(2,5-dihydroxy)phenylene}, poly(p-phenylene-2, 6-benzobisoxazole), poly(hexamethyleneadipamide), poly(4-aminobutyric acid), polyesters, poly(ethylene terephthalate), poly(butylene terephthalate), poly(1 ,4 cyclohexylidene dimethylene

terephthalate), polyvinyl alcohols, thermotropic liquid crystal polymers (LCP), polyolefins and homopolymers and copolymers of polyethylene and/or polypropylene.

The article of any one of the preceding claims wherein the fibers are made of ultrahigh molecular weight polyethylene (UHMWPE).

The article of any one of the preceding claims wherein the panel is prepared by stacking and compressing two or more sheets comprising monolayers of polymeric fibers.

The article of any one of the preceding claims wherein the panel contains a compressed stack of monolayers, each monolayer containing unidirectionally aligned fibers, preferably UHMWPE fibers, more preferably UHMWPE tapes, and optionally a binder in at most 20 wt% of the total weight of the monolayer, the fiber direction in each monolayer being rotated with respect to the fiber direction in an adjacent monolayer, the monolayers having a fiber weight of preferably between 25 and 150 gr/m², and wherein the compressed stack of monolayers has an experimental density (PEXP) of at least 90.0%, preferably of at least 95.0%, more preferably of at least 98.0% of the theoretical maximum density.

The article of any one of the preceding claims wherein the areal density (AD) of the panel is at least 1 kg/m². The article of any one of the preceding claims wherein the back face component contains at least one sheet comprising polymeric fibers.

The article of any one of the preceding claims wherein the back face component contains at least one sheet comprising polymeric fibers, each sheet comprising a plurality of monolayers, each monolayer containing unidirectionally aligned fibers or woven fibers.

The article of any one of the preceding claims wherein the areal density of the back face component (AD_BF) and the areal density of the strike face component (AD_SF) fulfil the relationship 0.5xAD_BF < AD_SF < 2xAD_BF.

The article according to any one of claims 1 -9 wherein the areal density of the back face component (AD_BF) is substantially the same with the areal density of the strike face component (AD_SF)

The article according to any one of claims 1 -1 1 wherein the areal density of the back face component (AD_BF) is at least 20% of the areal density of the article.

A device comprising an assembly of parts, wherein at least one part contains the article of any one claims 1 -12, said device being a piece of equipment of a mechanism.

A product comprising the article of any one claims 1 -12 wherein the product is chosen out of the group consisting of anti-ballistic vests, helmets, garments, blankets, shields, car parts, ballistic vehicle protection, windows, doors, (pseudo-)walls.

A method for life protection, wherein the ballistic resistant article of any one claims 1 -12 or the device according to claims 12 or 13, is positioned between a life-threat e.g. a projectile or explosive fragment, and a human, or an animal, or a human and an animal, in such a way to cover in full at least vital parts of the body of the human, or of the body of the animal, or the bodies of the human and the animal.