Multilayered material sheet and process for its preparation

Abstract

The invention relates to a multilayered material sheet comprising a consolidated stack of unidirectional monolayers of drawn polymer. The draw direction of two subsequent monolayers in the stack differs. Moreover the strength to thickness ratio of at least one monolayer is larger than 4.5.10.sup.13 N/m.sup.3. The invention also relates to a ballistic resistant article comprising the multilayered material sheet and to a process for the preparation of the ballistic resistant article.

Claims

1. A ballistic resistant article comprising a multilayered material sheet comprising: a consolidated stack of multiple unidirectional film monolayers comprised of a plurality of drawn anti-ballistic polymer film tapes having a stretch factor of at least 9 and a tensile strength of at least about 1.2 GPa, wherein adjacent monolayers in the stack have respective draw directions which differ from one another, and wherein the film tapes in the stack have an areal density of from 5 g/m.sup.2 to less than 50 g/m.sup.2 and a strength to thickness ratio which is larger than 4.510.sup.13 N/m.sup.3.

2. The ballistic resistant article according to claim 1, wherein the film tapes or monolayers have a strength to thickness ratio which is larger than 710.sup.13 N/m.sup.3.

3. The ballistic resistant article according to claim 1, which comprises a binder.

4. The ballistic resistant article according to claim 1, wherein the thickness of the film monolayers is between 3 and 25 m.

5. The ballistic resistant article according to claim 4, wherein the tensile strength of the drawn film tapes in the film monolayers is at least about 4 GPa.

6. The ballistic resistant article according to claim 1, wherein the polymer comprises ultra high molecular weight polyethylene.

7. The ballistic resistant article according to claim 1, wherein the draw directions of the adjacent monolayers in the stack differ by an angle of between 45 and 135.

8. The ballistic resistant article according to claim 1, wherein adjacent drawn film tapes in the film monolayers do not overlap.

9. The ballistic resistant article according to claim 1, wherein at least one of the film monolayers comprises a plurality of woven unidirectional film tapes of the drawn polymer.

10. The ballistic resistant article according to claim 1, comprising at least 4 unidirectional monolayers.

11. The ballistic resistant article according to claim 1, comprising a further sheet of material selected from the group consisting of ceramic, steel, aluminum, magnesium titanium, nickel, chromium and iron or their alloys, glass and graphite, or combinations thereof.

12. The ballistic resistant article according to claim 11, wherein the further sheet of material is positioned at an outside of the stack of monolayers at least at a strike face thereof.

13. The ballistic resistant article according to claim 11, wherein the further sheet of inorganic material has a thickness which is at most 50 mm.

14. The ballistic resistant article according to claim 11, further comprising a bonding layer between the material sheet and the further sheet of material, wherein the bonding layer comprises a woven or non-woven layer of inorganic fibers.

15. The ballistic resistant article according to claim 1, wherein the drawn anti-ballistic polymer film tapes have a stretch factor of at least 25.

16. The ballistic resistant article according to claim 7, wherein the angle is between 80 and 100.

17. The ballistic resistant article according to claim 1, wherein the ballistic resistant article has an E-abs ballistic performance value which is at least twice the E-abs ballistic performance value of an identical comparative ballistic resistant article of the same areal density but having monolayers in the stack with a strength to thickness ratio lower than 4.510.sup.13 N/m.sup.3 determined after two stops and two penetrations of the articles with 9 mm parabellum projectiles and 17 grain fragment simulating projectiles (FSP).

18. The ballistic resistant article according to claim 1, wherein the ballistic resistant article has an E-abs ballistic performance value which is at least twice the E-abs ballistic performance value of an identical comparative ballistic resistant article of the same areal density but having film tapes in the stack which have an areal density of greater than 50 g/m.sup.2 determined after two stops and two penetrations of the articles with 9 mm parabellum projectiles and 17 grain fragment simulating projectiles (FSP).

19. The ballistic resistant article according to claim 1, wherein the film tapes in the stack have an areal density of less than 29 g/m.sup.2.

20. The ballistic resistant article according to claim 1, wherein the film tapes in the stack have an areal density of less than 25 g/m.sup.2.

21. A process for the manufacture of a ballistic resistant article according to claim 1 comprising: (a) stacking the multilayered material sheet and a sheet of material selected from the group consisting of ceramic, steel, aluminum, titanium, glass and graphite, or combinations thereof; and (b) consolidating the stacked sheets under temperature and pressure.

Description

EXAMPLES

Examples 1 & 2Production of Tape

(1) An ultrahigh molecular weight polyethylene (UHMWPE) with an intrinsic viscosity of 20 was mixed to become a (7 wt %) suspension with decalin. The suspension was fed to an extruder and mixed at a temperature of 170 C. to produce a homogeneous gel. The gel was then fed through a slot die with a width of 600 mm and a thickness of 800 m. After being extruded through the slot die, the gel was quenched in a water bath, thus creating a gel-tape. The gel tape was stretched by a factor of 3.85 after which the tape was dried in an oven consisting of two parts at 50 C. and 80 C. until the amount of decalin was below 1%. This dry gel tape was wound on a coil for later treatment.

(2) The later treatment consisted of two stretching steps. The first stretching step was performed with a length of 20 meter tape in an oven at 140 C., with a stretching ratio of 5.8. The tape was reeled up and fed through an oven again. The second stretching step was performed at an oven temperature of 150 C. to achieve an additional stretching ratio of 6. The resulting tape had a width of 20 mm and a thickness of 12 micron.

(3) Performance Testing of the Tape

(4) The tensile properties of the tapes were tested by twisting the tape at a frequency of 38 twists/meter to form a narrow structure that is tested as for a normal yarn. Further testing was in accordance with 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.

Examples 1 & 2Production of Armor Panels from the Tape

(5) A first layer of tapes was placed, with parallel tapes adjacent to each other. A second layer of adjacent parallel tapes was placed on top of the first layer, whereas the tapes of the second layer were perpendicular to the tapes of the first layer. Subsequently, a third layer was placed on top of the second layer, again perpendicular to that second layer. The third layer was placed with a small shift (about 5 mm) as compared to the first layer. The shift was a half tape width. This shift was applied to minimize a possible accumulation of tape edges at a certain location. A forth layer was placed perpendicular to the third layer, with a small shift as compared to the second layer. The procedure was repeated until an areal density (AD) of 2.57 kg/m.sup.2 was reached. The stacks of layered tapes were moved into a press and pressed at a temperature of 145 C. and a pressure of 300 Bar for 65 minutes. Cooling was performed under pressure until a temperature of 80 C. was reached. No bonding agent was applied to the tapes. Nevertheless, the stacks had been fused to a rigid homogeneous 800400 mm plate.

(6) Performance Testing of the Armoured Panels

(7) The armoured plates were subjected to shooting tests performed with 9 mm parabellum bullets (Example 1) or 17 grain (1.1 gram) Fragment Simulating Projectiles (FSP: Example 2). Both tests were performed with the aim of determining a V50 and/or the energy absorbed (E-abs). V50 is the speed at which 50% of the projectiles will penetrate the armoured plate. The testing procedure was as follows. The first projectile was fired at the anticipated V50 speed. The actual speed was measured shortly before impact. If the projectile was stopped, a next projectile was fired at an intended speed of about 10% higher. If it perforated, the next projectile was fired at an intended speed of about 10% lower. The actual speed of impact was always measured. This procedure was repeated until at least 2 stops and 2 perforations were obtained. V50 was the average of the two highest stops and the two lowest perforations. The performance of the armour was also determined by calculating the kinetic energy of the projectile at V50 and dividing this by the AD of the plate (E-abs).

(8) Results:

(9) TABLE-US-00001 Strength/ Example; E-abs Thick- Thickness Compar. V50 J/(kg/ ness Strength (10.sup.13) Exp. Projectile m/s m.sup.2) m GPa N/m.sup.3 1 9 mm 563 498 12 2.5 21 parabellum 2 17 grain 64 12 2.5 21 FSP A 9 mm 250 65 2.8 4.3 parabellum B 17 grain 31 65 2.8 4.3 FSP

(10) Comparative experiments A, B were performed on sheets formed from commercially available ultrahigh molecular weight polyethylene (UHMWPE) unidirectional fiber. The fibers were impregnated and bonded together with 20 wt % of a thermoplastic polymer. The strength of the monolayers in comparative experiments A, B was 2.8 GPa, which is the strength of the fibers times the fiber content in the monolayer. The monolayers of the comparative experiments were compressed at about 125 C. under 165 bar pressure for 65 minutes to produce a sheet with the required areal density. The thickness of the monolayers after compressing was 65 micron.

(11) The results confirm that a multilayered material sheet with a strength to monolayer thickness ratio of greater than 4.510.sup.13 N/m.sup.3 exhibits improved antiballistic performance compared to multilayered material sheets of the prior art. In particular, the multilayered material sheet of the present invention produces an E-abs values of about twice as much as comparative samples from the prior art.