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 process for producing a ballistic-resistant molded article, wherein the molded article 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 the process comprises: 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 process according to claim 1, wherein the pressure of step c) is at least 10 MPa.

3. The process 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 process 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 process 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 process according to claim 1, further comprising, before step a), step a′) 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 process according to claim 6, wherein step a′) comprising 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 process 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 process 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 absent at from 45° to 135° relative to each other.

Description

EXAMPLES

Example 1

(1) 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 2000N/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.

(2) 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.

(3) 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.

(4) 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

(5) A molded article was produced according to Example 1, except that a pressure of 8 MPa was applied.

Example 3

(6) A molded article was produced according to Example 1, except that a pressure of 16 MPa was applied.

(7) Comparative Experiment A

(8) 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.

(9) Comparative Experiment B

(10) A molded article was produced according to Comparative Experiment A, except that a pressure of 8 MPa was applied.

(11) Comparative Experiment C

(12) A molded article was produced according to Comparative Experiment C, except that a pressure of 16.5 MPa was applied.

(13) TABLE-US-00001 TABLE 1 Ex- Areal Pres- Thick- ample density sure ness .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. 13.0 2 14.3 9 653 131 Ex. A C. 13.0 8 13.4 9 724 161 Ex. B C. 13.0 16.5 13.0 9 810 201 Ex. C 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

(14) 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.

(15) Comparative Experiment D

(16) 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

(17) Comparative Experiment D was repeated but using 7 wt. % Queo 1007 powder.

Example 5

(18) Comparative Experiment D was repeated but using 10 wt. % Queo 1007 powder.

(19) 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

(20) 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.