IMPACT RESISTANT COMPOSITE MATERIAL

Abstract

The invention relates to a preformed sheet, comprising a network of polyethylene fibers having a tensile strength of at least 1.5 GPa, impregnated with at least 10% of a plastic wherein the plastic material is an acrylic based thermoplastic material with a glass transition temperature of at least 25? C. The invention further relates to an assembly of at least two preformed sheets and to a ballistic resistant article comprising at least one assembly.

Claims

1. Preformed sheet, comprising a network of polyethylene fibers having a tensile strength of at least 1.5 GPa, impregnated with at least 10% of a plastic material characterized in that the plastic material is an acrylic based thermoplastic material with a glass transition temperature of at least 25? C.

2. Preformed sheet according to claim 1, wherein the network of fibers comprises a fabric.

3. Preformed sheet according to claim 1 wherein the network of fibers comprises unidirectionally aligned fibers.

4. Preformed sheet according to claim 1, wherein the fibers are UHMWPE fibers.

5. Preformed sheet according to claim 1, wherein the preformed sheet comprises a separating film on at least one of its outer surfaces.

6. Preformed sheet according to claim 5, wherein the separating film is a biaxially stretched polyolefin film.

7. Assembly of at least two preformed sheets according to claim 1, which sheets are substantially not linked to one another.

8. Ballistic resistant article comprising at least one assembly according to claim 7.

9. Ballistic resistant article comprising a plurality of preformed sheets according to claim 2 having an Eabs of more than 180 J/kg/m.sup.2 for 9 mm*19 Natoball DM11 A1B2 bullet.

10. Ballistic resistant article according to claim 9, further comprising at least two networks of unidirectionally aligned fibers with optionally a matrix.

11. Ballistic resistant article according to claim 10, wherein the matrix for the unidirectional aligned fibers comprises a modified polyolefin, a SIS, or a SEBS.

12. Ballistic resistant article according to claim 10, wherein the matrix for the unidirectional aligned fibers comprises a polyurethane.

13. Ballistic resistant article according to claim 10, wherein the matrix for the unidirectional aligned fibers is an acrylic based thermoplastic material with a glass transition temperature of at least 25? C.

14. Use of an acrylic based thermoplastic material with a glass transition temperature of at least 25? C. in the manufacture of ballistic resistant composites.

15. Use of an acrylic based thermoplastic material with a glass transition temperature of at least 25? C. in the manufacture of ballistic resistant composites comprising polyethylene fibers.

Description

EXAMPLE I

[0053] A mono-layer was produced from Dyneema? UHMWPE fibers with a strength of 3.5 GPa in the same way as for comparative experiment A. In this case a Neocryl? from DSM Neoresins was used as matrix material. After drying, the obtained mono-layer contained 33 gram of parallel (unidirectional) aligned UHMWPE fibers and 16 wt % of Neocryl? (methylmethacrylate acrylic copolymer with a Tg of 35? C.) as matrix material. A preformed sheet was produced in the same way as Comparative Experiment A by stacking 4 monolayers and one outer Stamylex? linear low-density polyethylene film.

[0054] A flat ballistic-resistant article was made from a loose, non-linked assembly of a number of preformed sheets, the assembly being stitched through at the corners.

[0055] The downward deflection is 68 mm, which is lower than the 137 mm for Comparative Experiment A, hence indicating a higher stiffness of the sheets of Example 1.

TABLE-US-00001 TABLE 1 Experiment/ Weight V50 Eabs Downward deflection Example [kg/m.sup.2] [m/s] [J/kg/m.sup.2] [mm] A 3.3 376 170 137 I 3.3 425 217 68

[0056] Table 1 shows that despite the higher stiffness of the sheet according to the invention, a higher projectile stopping performance could be reached. This is against the common belief that best projectile stopping performance is achieved with a soft (i.e. not stiff) matrix system and sheets.