BALLISTIC-RESISTANT MOLDED ARTICLE

Abstract

The present invention provides process for producing a ballistic-resistant molded article, which molded article comprises: i) a plurality of layers of unidirectionally aligned polyolefin fibers, which layers are substantially absent a bonding matrix; and ii) a plurality of layers of adhesive, and which process comprises: a) providing a plurality of precursor sheets, each of said precursor sheets comprising i) at least one layer of unidirectionally aligned polyolefin fibers which layer is substantially absent a bonding matrix, and ii) at least one layer of adhesive; b) stacking said precursor sheets to form a stack, wherein the total amount of adhesive in the stack is from 5.0 to 12.0 wt. % based on the total weight of the stack; c) pressing the stack produced in step b) at a temperature of from 1 to 30° C. below the melting point of the polyolefin fibers and at a pressure of at least 8 MPa; and d) cooling the pressed stack produced in step c) to at least 50° C. below the melting point of the polyolefin fibers while maintaining pressure.

Claims

1. A ballistic-resistant molded article which comprises: i) a plurality of layers of unidirectionally aligned fused polyolefin fibers, which layers are substantially absent a bonding matrix; and ii) a plurality of layers of adhesive between adjacent layers of the unidirectionally aligned fused fibers, and wherein wherein the ballistic-resistant molded article is obtained by a process comprising: a) providing a plurality of precursor sheets, each of said precursor sheets comprising: i) at least one layer of unidirectionally aligned fused polyolefin fibers, wherein the at least one layer is substantially absent of a bonding matrix, and ii) at least one layer of adhesive; b) stacking the precursor sheets to form a stack, wherein the total amount of the adhesive in the stack is from 5.0 to 12.0 wt. % based on the total weight of the stack; c) pressing the stack produced in step b) at a temperature of from 1 to 30° C. below the melting point of the polyolefin fibers and at a pressure of at least 8 MPa; and d) cooling the pressed stack produced in step c) to at least 50° C. below the melting point of the polyolefin fibers while maintaining pressure.

2. The ballistic-resistant molded article according to claim 1, wherein the pressure of step c) is at least 10 MPa.

3. The ballistic-resistant molded article according to claim 1, wherein the total amount of the adhesive present is from 6.0 to 11.0 wt. % based on the total weight of the stack.

4. The ballistic-resistant molded article according to claim 1, wherein step b) comprises orienting each layer of the unidirectionally aligned fused polyolefin fibers which layer in which a bonding matrix is substantially absent at an angle of from 45° to 135° with respect to an orientation of the unidirectionally aligned fused polyolefin fibers of an adjacent layer of polyolefin fibers in which a bonding matrix is substantially absent.

5. The ballistic-resistant molded article according to claim 1, wherein step b) comprises separating each layer of the unidirectionally aligned fused polyolefin fibers in which a bonding matrix is substantially absent from an adjacent layer of the unidirectionally aligned fused polyolefin fibers in which a bonding matrix is absent by a layer of adhesive.

6. The ballistic-resistant molded article according to claim 1, wherein the process further comprises, before step a), a step a′) of producing a precursor sheet which comprises: i) at least one layer of unidirectionally aligned fused polyolefin fibers in which a bonding matrix is substantially absent, and ii) at least one layer of adhesive; by applying a layer of adhesive to a layer of unidirectionally aligned fused polyolefin fibers in which a bonding matrix is substantially absent.

7. The ballistic-resistant molded article according to claim 6, wherein step a′) comprises applying from 5.0 to 12.0 wt % adhesive to the layer of the unidirectionally aligned fused polyolefin fibers in which a bonding matrix is substantially absent a bonding matrix, based on the total weight of the layer and the adhesive.

8. The ballistic-resistant molded article according to claim 7, wherein step a′) further comprises consolidating two layers of the unidirectionally aligned fused polyolefin fibers in which a bonding matrix is substantially absent, and a layer of adhesive, wherein the layers of unidirectionally aligned fused polyolefin fibers are separated by the layer of adhesive.

9. The ballistic-resistant molded article according to claim 8, wherein step a′) comprises orienting the two layers of the unidirectionally aligned fused polyolefin fiber in which a bonding matrix is substantially at from 45° to 135° relative to each other.

10. A ballistic-resistant molded article, which comprises: i) a plurality of layers of unidirectionally aligned polyolefin fibers, which layers are substantially absent a bonding matrix; and ii) a plurality of layers of adhesive, wherein the total amount of adhesive present is from 5.0 to 12.0 wt. % based on the total weight of the ballistic-resistant molded article.

11. The ballistic-resistant molded article according to claim 10, wherein the ballistic resistant article comprises from 6.0 to 11.0 wt. % of adhesive based on the total weight of the ballistic-resistant molded article.

12. A ballistic-resistant molded article according to claim 11, which ballistic-resistant molded article has a consolidation parameter (.sup.140T.sub.16.5-2) of less than 7%; wherein .sup.140T.sub.16.5-2 is the reduction in thickness of the plurality of layers of unidirectionally aligned polyolefin fibers which layers are substantially absent a bonding matrix and plurality of layers of adhesive when subjected to a pressure of 16.5 MPa at 140° C. based on the thickness when subjected to a pressure of 2 MPa at 140° C.

13. A ballistic-resistant molded article according to claim 12, wherein the ballistic-resistant molded article has an areal density of at most 11 Kgm.sup.−2 and meets NIJ level III.sup.+ performance against 7.62×39 mm MSC (AK47).

14. A precursor sheet comprising: i) at least two layers of unidirectionally aligned polyolefin fibers, wherein the at least two layers are substantially absent of a bonding matrix; and ii) at least two layers of adhesive, wherein each of the at least two layers of unidirectionally aligned polyolefin fibers which are substantially absent a bonding matrix are separated by one layer of adhesive which is present in an amount of from 5.0 to 12.0 wt. % based on the total weight of the precursor sheet.

Description

EXAMPLES

Example 1

[0080] A precursor sheet was produced from 40 yarns of Dyneema® SK76 1760 dtex yarn, available from DSM Dyneema, Heerlen, Netherlands. Yarn was unwound from bobbins on a tension controlled creel and passed through a reed. Subsequently the yarns were spread to form a gap-less bed of filaments with a width of 320 mm by feeding the yarns over a spreading unit. The spread yarns were then fed into a calender. The rolls of the calender had a diameter of 400 mm and the applied line pressure was 2000 N/cm. The line operated at a line speed of 8 m/min and at a roll surface temperature of 154° C. In the calender the yarns were fused into a fibrous tape. The tape was removed from the calender by the first roller-stand. A powder scattering unit was placed between the calender and the first roller-stand applying 7 wt. % Queo 1007 powder, available form Borealis, Vienna, Austria to the upper surface of the tape. The tape with powder was calendered at elevated temperature and wound onto a roller stand.

[0081] A fibrous tape with a width of 320 mm and a thickness of 46 μm was obtained. The fibrous tape had a tenacity of 35.4 cN/dTex and a modulus of 1387 cN/dTex.

[0082] Five of said tapes were aligned in parallel and abutting to form 1600 mm wide sheet. A second, identical, sheet of five tapes was formed on top of the first sheet, with the adhesive layers of both sheets facing upwards, but with the fibers aligned perpendicularly. A two-layered, cross-plied sheet having an areal density of 95 gm.sup.−2 resulted. This sheet was cut into 400 mm×400 mm square precursor sheets. Multiple square precursor sheets were stacked, making sure the alternating 0°/90° direction of the tape layers was maintained. The stack of precursor sheets was processed into a molded article of 9.8 Kgm.sup.−2. The molded article contained 206 layers of unidirectional aligned tapes. The stack of sheets was pressed into a molded article at 2 MPa and 145° C. for 40 minutes followed by a cooling period of 20 min at 2 MPa.

[0083] The molded article was shot with a 7.62×39 mm MSC (AK47) bullet in order to determine V.sub.50. Results are listed in Table 1, below.

Example 2

[0084] A molded article was produced according to Example 1, except that a pressure of 8 MPa was applied.

Example 3

[0085] A molded article was produced according to Example 1, except that a pressure of 16 MPa was applied.

Comparative Experiment A

[0086] 400 mm×400 mm sheets of unidirectionally aligned fiber layers, available as HB210 from DSM Dyneema, Heerlen, Netherlands, were stacked to form an assembly having an areal density of 13.0 Kgm.sup.−2. The sheets each comprised 4 layers, each layer comprising unidirectionally aligned fibers of UHMWPE embedded in a matrix of 17% of a polyurethane resin, and layered in the configuration of fiber direction 0°/90°/0°/90°. In total, 96 sheets were used, with the alternating 0°/90° direction of adjacent layers maintained throughout the stack. The assembly of sheets was pressed at 2 MPa and 125° C. for 40 minutes followed by a cooling period of 20 min at 2 MPa. A molded article having an areal density of 13.0 Kgm.sup.−2 resulted. The molded article was shot with a 7.62×39 mm MSC (AK47) bullet in order to determine V.sub.50. Results are listed in Table 1, below.

Comparative Experiment B

[0087] A molded article was produced according to Comparative Experiment A, except that a pressure of 8 MPa was applied.

Comparative Experiment C

[0088] A molded article was produced according to Comparative Experiment C, except that a pressure of 16.5 MPa was applied.

TABLE-US-00001 TABLE 1 Areal Example density Pressure Thickness .sup.140T.sub.16.5-2 V.sub.50 E.sub.abs no. [Kgm.sup.−2] [MPa] [mm] [%] [ms.sup.−1] [JKg.sup.−1m.sup.2] C. Ex. A 13.0 2 14.3 9 653 131 C. Ex. B 13.0 8 13.4 9 724 161 C. Ex. C 13.0 16.5 13.0 9 810 201 Ex. 1 9.8 2 10.4 3 627 160 Ex. 2 9.8 8 10.2 3 710 205 Ex. 3 9.8 16.5 10.1 3 793 256

[0089] These results show that, for a ballistic-resistant molded article consisting of a material according to the present invention, an E.sub.abs of over 200 may be achieved by applying a pressure of only 8 MPa; whereas for a molded article according to the prior art, a pressure of 16.5 MPa is required to achieve an E.sub.abs of over 200. Further, increasing the pressure applied to achieve this performance from a pressure of 2 MPa to 16.5 MPa, leads to a reduction in thickness of from only 10.4 to 10.1 mm in the material of the present invention; whereas a reduction in thickness of from 14.3 to 13.0 is observed in the Comparative Examples.

Comparative Experiment D

[0090] Example 1 was repeated but using 4 wt. % Queo 1007 powder and instead stacking only enough precursor sheets to produce a 400 mm by 400 mm molded article having an areal density of 6.8 Kgm.sup.−2. Molded articles were shot with 9 mm (Remington) ammunition to determine Back Face Signature (BFS). Results are given in Table 2, below.

Example 4

[0091] Comparative Experiment D was repeated but using 7 wt. % Queo 1007 powder.

Example 5

[0092] Comparative Experiment D was repeated but using 10 wt. % Queo 1007 powder.

TABLE-US-00002 TABLE 2 Example no. wt. % adhesive BFS [mm] C. Ex. D 4 6.3 Ex. 4 7 3.4 Ex. 5 10 3.4

[0093] These results show that surprisingly back face deformation is reduced in Examples 4 and 5 according to the present invention, compared with a molded article having a higher wt. % of adhesive (Comparative Experiment D), which adhesive is impregnated into the fiber layers. Further, the difference between Example 4 and Example 5, did not indicate any improvement in BFS resulting from the addition of 10% matrix rather than 7% matrix.