Mutilayered material sheet and process for its preparation

Abstract

The invention relates to a multilayered material sheet comprising a consolidated stack of unidirection monolayers of drawn ultra high molecular weight polyolefine. The draw direction of two subsequent monolayers in the stack differs. Moreover the thickness of at least one monolayer does not exceed 50 m, and the strength of at least one monolayer is comprised between 1.2 GPa and 3 GPa. 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 multilayered material sheet comprising a consolidated stack of unidirectional monolayers produced from a plurality of drawn ultra high molecular weight polyolefin tapes, wherein a draw direction of two subsequent monolayers in the stack differs, and wherein an areal density of at least one monolayer is between 3 and 200 g/m.sup.2 and an areal density of at least one drawn ultra high molecular weight polyolefin tape is between 10 and 80 g/m.sup.2, and wherein at least one monolayer of the stack has a strength which is at least 1.2 GPa, and wherein the plurality of drawn tapes are aligned in the same direction and adjacent ones of the tapes do not overlap.

2. The material sheet according to claim 1, wherein the areal density of the tape is between 15 and 60 g/m.sup.2.

3. The material sheet according to claim 1, wherein the polyolefin is ultrahigh molecular weight polyethylene (UHMWPEI and the areal density of the tape is less than 50 g/m.sup.2.

4. The material sheet according to claim 1, wherein the areal density of the at least one unidirectional monolayer is between 5 and 120 g/m.sup.2.

5. The material sheet according to claim 1, wherein the areal density of the at least one monolayer is between 10 and 80 g/m.sup.2.

6. The material sheet according to claim 1, wherein the at least one monolayer has a thickness which does not exceed 29 m.

7. The material sheet according to claim 1, wherein the at least one monolayer has a strength which is between 1.2 GPa and 3 GPa.

8. The material sheet according to claim 1, wherein the polyolefin comprises ultra high molecular weight polyethylene.

9. The material sheet according to claim 1, wherein two subsequent monolayers in the stack have respective draw directions which differ by an angle of between 45 and 135.

10. The material sheet according to claim 1, wherein the at least one monolayer comprises gel-spun polyolefin tapes having a width of at least 2 mm and an areal density of between 3 and 200 g/m.sup.2.

11. The material sheet according to claim 1, wherein the at least one monolayer comprises a plurality of unidirectional tapes of the drawn polyolefin, and wherein the unidirectional tapes form a woven fabric.

12. A ballistic resistant article comprising the material sheet according to claim 1.

13. The ballistic resistant article according to claim 12, comprising at least 10 unidirectional monolayers.

14. The ballistic resistant article according to claim 12, 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.

15. The ballistic resistant article according to claim 14, wherein the further sheet of material has a thickness which is at most 50 mm.

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

Description

EXAMPLE AND COMPARATIVE EXPERIMENT

Example

Production of Tape

(1) An ultrahigh molecular weight polyethylene 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 3.8 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 subsequently stretched in an oven at 140 C., with a stretching ratio of 5.8, followed by a second stretching step at an oven temperature of 150 C. to achieve an final thickness of 18 micrometer.

Performance Testing of the Tape

(2) The tensile properties of the tape was 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 fibre of 500 mm, a crosshead speed of 50%/min and Instron 2714 clamps, of type Fibre Grip D5618C.

Example

Production of Armor Panels From the Tape

(3) 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 directions of the tapes in the second layer were perpendicular to the direction of 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. 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.

Performance Testing of Armored Panels

(4) The armoured plates were subjected to shooting tests performed with 9 mm parabellum bullets. The 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 fires at an intended speed of about 10% lower. The actual speed of impact was always measured. 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).

RESULTS

(5) TABLE-US-00001 Example; Compartive V50 E-abs Thickness Strength Experiment m/s J/(kg/m.sup.2) m GPa 1 526 388 18 2.2 A 423 250 65 3.7

(6) Comparative experiment A was 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 experiment A was 2.8 GPa, which is the strength of the fibers times the fiber content in the monolayer. The monolayers of the comparative experiment 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.

(7) The results confirm that a multilayered material sheet with monolayers not exceeding 50 m and having a monolayer strength of at least 1.2 GPa produces unexpectedly improved anti-ballistic performance compared to armoured sheets produced from conventional UD fibre based multilayered sheets. In particular, the multilayered material sheet of the present invention produced a significant higher E-abs value than a comparative sample from the prior art.