PREFORMED SHEET AND BALLISTIC-RESISTANT ARTICLE

Abstract

The invention relates to a preformed sheet comprising mono-layers from a fibrous network with fibers having a tensile strength of at least about 1.2 GPa and preferably a binder, and a separating film on at least one of its outer surfaces, the separating film having an areal density of between 1 and 10 g/m.sup.2 and a surface tension of less than 35 mN/m at the surface faced to the fibrous network and the separating film has a crystallinity of between 50 and 90%.

Claims

1. Preformed sheet comprising one, preferably at least two, mono-layers, each mono-layer containing a fibrous network with fibers having a tensile strength of at least about 1.2 GPa and a binder, and a separating film on at least one of its outer surfaces, the separating film, substantially free of voids or porosity, having an areal density of between 1 and 10 g/m.sup.2, characterized in that the separating film has a surface tension of less than 35 mN/m at the surface faced to the fibrous network and the separating film has a crystallinity of between 50 and 90%.

2. Preformed sheet according to claim 1, wherein the mono-layer is to a layer of unidirectionally oriented fibers.

3. The preformed sheet according to claim 2, comprising at least 2 mono-layers, with the fiber direction of adjacent layers is rotated to each other.

4. Preformed sheet according to claim 1, wherein the fibers comprise ultra-high molar mass polyethylene.

5. Preformed sheet according to claim 1, wherein the binder is a thermoplastic polyolefin.

6. Preformed sheet according to claim 1, wherein the binder is Styrene Ethylene Butylene Styrene Copolymer (SEBS) or Styrene Isoprene Styrene (SIS).

7. The preformed sheet according to claim 1, wherein the separating film is a biaxially stretched polyolefin film.

8. Preformed sheet according to claim 7, wherein the separating film is a biaxially stretched polypropylene (BOPP) film.

9. Assembly of at least two preformed sheets according to claim 1.

10. Ballistic-resistant article comprising at least one assembly or a preformed sheet according to claim 1.

11. Flexible ballistic-resistant article according to claim 10, the assembly or the preformed sheet having an areal density less than 4.75 kg/m.sup.2 and V.sub.50 of at least 600 m/s against 9 mm, wherein the article has a 9 mm V.sub.50 retention after 24 hours soaking in salt water, and after 4 hours in JP8 fuel of at least 85%.

12. Use of a separating film in the manufacturing of a flexible ballistic-resistant article comprising a fibrous network with fibers having a tensile strength of at least about 1.2 GPa, characterized in that the separating film is a biaxially stretched polymer film with an areal density of between 1 and 10 g/m.sup.2, a surface tension of less than 35 mN/m at the surface faced to the fibrous network and a crystallinity of between 50 and 90%.

13. Use of a separating film in the manufacturing of a flexible ballistic-resistant article comprising a fibrous network with fibers having a tensile strength of at least about 1.2 GPa, characterized in that the separating film is a biaxially stretched polyolefin film with an areal density of between 1 and 10 g/m.sup.2, a surface tension of less than 35 mN/m at the surface faced to the fibrous network and a crystallinity of between 50 and 90%.

14. Use of a separating film in the manufacturing of a flexible ballistic-resistant article comprising a fibrous network with fibers having a tensile strength of at least about 1.2 GPa, characterized in that the separating film is a biaxially stretched polypropylene film with an areal density of between 1 and 10 g/m.sup.2, a surface tension of less than 35 mN/m at the surface faced to the fibrous network and a crystallinity of between 50 and 90%.

Description

COMPARATIVE EXPERIMENT A

[0050] A unidirectional monolayer was formed from UHMWPE fibers. The yarns, as commercially available from DSM Dyneema in the Netherlands with a tensile strength of 4.1 GPa, were oriented in parallel and held together by about 17 mass % (of the total mass of the monolayer) of a polyurethane elastomeric matrix material as described in the examples of WO04039565 A1. A sheet was produced by using 2 stacked unidirectional monolayers in a 0-90 orientation, containing two 7 m thick polyethylene (LDPE) films sandwiching the stack of 2 monolayers, laminated together resulting in a sheet having an areal density (AD) of 80 g/m.sup.2. The polyethylene film had a crystallinity of about 45%.

COMPARATIVE EXPERIMENT B

[0051] Comparative Experiment A was repeated, but now the resin matrix was a based on Kraton D1107 (polystyrene-polyisoprene-polystyrene block copolymer thermoplastic elastomer) and the separating film a biaxially stretched polypropylene film, having a crystallinity of about 55% and a surface tension of the side applied to the stack of monolayers of more than 37 mN/m, has a thickness of 10 m (Treofan PHD10).

[0052] FIG. 1 shows a picture of the assembly that has been soaked half way down 6 hours in seawater. The dotted line represents the immersion limit. The plain line shows the limit between dry area (top/white) and completely soaked area (bottom/grey) on the sheet. About 90% of the immersed surface is soaked with water,

EXAMPLE 1

[0053] Comparative Experiment B was repeated, but now the 10 m polypropylene separating film had the surface tension of the side applied to the stack of monolayers of less than 35 mN/m. Ambient V.sub.50 values where equal to that of Comparative Experiment B. The observed V.sub.50 retention after immersion in JP8 was 89%, significantly higher than that of Comparative Experiment A. In addition, V.sub.50 retention after immersion in salt water solution was 92%, significantly higher than those of Comparative Experiment A and Comparative Experiment B.

[0054] FIG. 2 shows a picture of the assembly that has been soaked half way down for 6 hours in salt water solution. The dotted line represents the immersion limit. The plain line shows the limit between dry area (white) and completely soaked area (grey) on the sheet. The surface soaked with water is about 25%. Table 3 shows that the weight gain of an assembly according to the invention is lower than 25%.

[0055] The overall ballistic performance of panel composed of a given material is defined by the lowest performance to one of the given threats. Consequently, Example 1 is seen having the greatest ballistic resistance compared to the Comparative Experiment A and B. At a given number of sheets, here being 55, Example 1 has a similar V.sub.50 in ambient condition than that of both Comparative Experiments, as seen in Table 1. However, the results in Table 2 clearly show the improved ballistic performance expressed in V.sub.50 retention. After 4 hours JP8 fuel immersion the V.sub.50 retention of Example 1 is at least 89%. After 24 hours soaking in salt water solution the V.sub.50 retention is at least 92%.

TABLE-US-00001 TABLE 1 9 mm Dry Film ballistic Film surface AD AD performance Polymeric Thickness tension sheet panels Relative Example Binder Film m mN/m g/m2 kg/m2 m/s V50 CEA PUR LDPE 7 <37 80 4.4 614 100% CEB Kraton BOPP 10 >37 85.5 4.71 598 98% E1 Kraton BOPP 10 <35 85.5 4.71 603 99%

TABLE-US-00002 TABLE 2 Performance after Performance after JP8 Immersion Salt Water Immersion 9 mm V50 9 mm V50 9 mm V50 retention 9 mm V50 retention Example m/s % m/s % CEA 472 77% 534 87% CEB 532 89% 501 84% E1 543 90% 556 92%

TABLE-US-00003 TABLE 3 Weight gain after 24 hours in salt water solution Example % CEA 27% CEB 44% E1 22%