High performance fibres composite sheet

Abstract

The invention relates to a method for manufacturing a composite sheet comprising high performance polyethylene fibres and a polymeric resin comprising the steps of assembling HPPE fibres to a sheet, applying an aqueous suspension of a polymeric resin to the HPPE fibres, partially drying the aqueous suspension, optionally applying a temperature and/or a pressure treatment to the composite sheet wherein the polymeric resin is a homopolymer or copolymer of ethylene and/or propylene. The invention further relates to composite sheets obtainable by said method and articles comprising the composite sheet such as helmets, radomes or a tarpaulins.

Claims

1. A method for manufacturing a composite sheet comprising high performance polyethylene fibres and a polymeric resin comprising the steps of: a) providing high performance polyethylene (HPPE) fibres with a tenacity of at least 1.0 N/tex; b) assembling the HPPE fibres to form a sheet; c) applying an aqueous suspension of the polymeric resin to the HPPE fibres before, during or after assembling; d) at least partially drying the aqueous suspension of the polymeric resin applied in step c); to obtain a composite sheet upon completion of steps a), b), c) and d); e) optionally applying a temperature in the range from the melting temperature of the resin to 153° C. to the sheet of step c) before, during and/or after step d) to at least partially melt the polymeric resin; and f) optionally applying a pressure to the composite sheet before, during and/or after step e) to at least partially compact the composite sheet, wherein the polymeric resin comprises a functionalized polymer which is a copolymer of ethylene and/or propylene with an ethylenically unsaturated monomer comprising a carboxylic acid group or derivative thereof, and wherein the polymeric resin has a density as measured according to ISO1183 in the range from 860 to 930 kg/m.sup.3, a peak melting temperature in the range from 40 to 140° C. and a heat of fusion of at least 5 J/g.

2. The method according to claim 1 wherein the HPPE fibres are selected from the list consisting of tapes, filaments and staple fibres.

3. The method of claim 1, wherein the HPPE fibres are prepared by a melt spinning process, a gel spinning process or solid state powder compaction process.

4. The method according to claim 1, wherein the concentration of polymeric resin in the aqueous suspension is between 4 and 60 wt %, wherein the weight percentage is the weight of polymeric resin in the total weight of aqueous suspension.

5. The method according to claim 1, wherein the HPPE fibres have a tenacity of at least 1.5 N/tex.

6. The method according to claim 1, wherein the HPPE fibres comprise ultra high molecular weight polyethylene (UHMWPE).

7. The method according to claim 1, wherein the amount of polymeric resin in the composite sheet is between 1 and 25 wt %, wherein the weight percentage is the weight of polymeric resin in the total weight of the composite sheet.

8. The method according to claim 1, wherein the ethylenically unsaturated monomer is selected from the group consisting of acrylic, methacrylic, cinnamic, crotonic, and maleic, fumaric, and itaconic reactants.

9. The method according to claim 1, wherein the peak melting temperature is in the range from 60 to 120° C.

10. The method according to claim 1, wherein the heat of fusion is at least 20 J/g.

11. The method according to claim 6, wherein the HPPE fibres comprise more than 95 wt. % of the UHMWPE.

12. The method of claim 7, wherein the amount of polymeric resin in the composite sheet is between 4 and 18 wt %.

13. The method according to claim 1, wherein the heat of fusion is at least 50 J/g.

Description

EXAMPLES 1 TO 3 AND COMPARATIVE EXPERIMENTS A AND B

(1) Oriented UHMWPE tape was produced according to the solid state powder process of EP1627719. The tapes of a thickness of 65 μm were slit along their orientation (drawing) direction to a width of 20 mm. 2 tapes of 20×200 mm.sup.2 (12) and a rectangular piece of 10×20 mm.sup.2 (14) were prepared (FIG. 1A) respecting the tape orientations (122) and (124) as depicted, for later assembly as shown in FIG. 1B. Assembly is such that the orientation direction (142) of the rectangular piece (14) is perpendicular to orientation direction (122) of the other 2 tapes (12). This difference of orientation direction is chosen, because perpendicular stacking is typical for armour and provides more critical adhesion values as compared to specimens with aligned orientations.

(2) Test sampled were prepared by brush coating the future contact surfaces of the tape samples (12) and (14) with suspensions 1 to 3, substantially evaporating the water from the suspension under ambient conditions during 20 minutes followed by assembling the individual pieces according to FIG. 1b and pressing the contact area with a flat metal plate at 139° C. and a mass of 5 kg for 30 seconds. Two Comparative Experiments A and B were prepared in an identical way with Suspension 4 and no suspension respectively.

(3) The obtained test samples tested at room temperature and at 70° C. and were clamped in a Zwick Z010 testing machine and loaded till fracture in the direction of the orientation direction of the tapes (122). The samples without suspension failed during the careful clamping operation and could not be tested.

(4) TABLE-US-00001 Fracture force [N] Fracture force [N] Suspension 23° C. 70° C. Example 1 1  98 n.a. Example 2 2 275 273 Example 3 3 359 294 Comp. Exp. A 4  34  22 Comp. Exp. B n.a. Not measurable Not measurable
The samples prepared with the polyolefin suspension show a substantially improved shear strength as compared to the test sample with the PUR or without suspension.

EXAMPLE 4

(5) A fibrous armor sheet material was made by impregnating a unidirectional layer of Dyneema® 1760 SK76 fibers with a polyolefin suspension prepared by blending suspension 1 in a 1:1 ratio with water. After drying the aerial density of the unidirectional layer was 65 g/m.sup.2 with a fiber to resin ratio of 82:18. Four such unidirectional layers were cross plied in a 0° 90° 0° 90° sequence and consolidated for 30 seconds at a pressure of 30 bar and a temperature of 115° C. The resulting cross plied sheet, bare of further protective films, had an areal density of 260 g/m.sup.2. The sheets were very robust and allowed easy handling and stacking for producing hard ballistic armors, plates or helmets.

EXAMPLE 5

(6) A stack of 28 sheets from Example 4 was made and pressed into a helmet shape in a deep draw mold with a gap of 7 mm. Pressing was performed during 30 minutes at 165 bar and 135° C. The pressure was maintained during cooling until the temperature was below 80° C. The helmets were trimmed to shape and subjected to shooting tests with 9 mm Parabellum bullets with a speed of 430 meters per second. The tests were performed with the NIJ Ballistic Penetration test Headform, Model 100_00_HNME according to N.I.J. 0106.01 standard for ballistic penetration tests using Herbin Sueu Plastiline clay. Two helmets were made and each helmet was subjected to four shots. The average depth of the four shots of each helmet was determined.

(7) Comparative Experiment C:

(8) 2 further helmets were produced and tested according to examples 5 with the difference that Dyneema® HB26, available from DSM Dyneema, was used. HB26 has an areal density of 264 g/m.sup.2, with a polyurethane matrix content of about 18 wt %.

(9) The shooting trauma depth were measured in the clay. The results are presented in the table below for each helmet:

(10) TABLE-US-00002 Trauma depth Example 5′ 12.6 mm Example 5″ 13.0 mm Comp. Ex. C′ 14.8 mm Comp. Ex. C″ 13.6 mm
The trauma depths of the helmets of Example 5 are smaller than the ones of the comparative experiment C. The average observed reduction of about 1.4 mm trauma depth is a significant improvement for combat helmets.

EXAMPLE 6

(11) The tapes of Examples 1 where cut to square pieces of 40×40 cm.sup.2. The tapes were wetted by spraying them with about 40 ml/m.sup.2 of suspension 1 diluted with water to a solid content of 4 wt %. 74 tapes were dried and stacked in an alternating 0° 90° sequence to a total areal density of 4.89 kg/m.sup.2. The stacks were pressed during 45 minutes at a temperature of 120° C. and a pressure of 165 bar. The stacks were cooled under pressure until a temperature of 80° C. was reached and then removed from the press.

(12) Comparative Experiment D:

(13) Example 6 was repeated by stacking 75 tape without the diluted suspension 1, resulting in a compressed stack with an areal density of 4.89 kg/m.sup.2. The compressed stacks of example 6 and Comparative Experiment D were subjected to shooting tests with 1.1 gram Fragment Simulating Projectiles. The speed of the projectiles was chosen such that a part of them perforated and a part of them were stopped, thus measuring in the range of the critical speed. The actual speed of the stopped projectiles was recorded and the width of the delaminated area of the corresponding stop locations was measured. The average stopping speeds and trauma width are presented in the table below:

(14) TABLE-US-00003 Comparative Example 6 Experiment D Average stopping speed [m/sec] 451 463 Average trauma width [mm] 81.5 89.4 trauma width/stopping speed [msec] 0.180 0.193

(15) The difference in stopping speed was small and probably not of statistical significance. However, the difference in trauma width is significant. Even after normalizing against the stopping speed, the trauma in the panels according to the invention is smaller. Reduction in trauma width in armour plates is important in view of multi-hit performance since small trauma width reduces the chance of a second hit to arrive at a pre-damaged location. Coherence of the armour plates after being hit is better.

EXAMPLE 7

(16) A Dyneema® fabric with an aerial density of 163 gram/m.sup.2 was wetted with a polyolefin suspension 1. A black die was added to the suspension before applying it to the fabric. After drying, a robust water tight flexible sheet was obtained with good impregnation of the fibers. The fibre to polyolefin ratio of the sheet was 0.88 (47 wt % fibers). A cross-sectional inspection of the impregnated fabric confirmed that the dyed polyolefin suspension was present throughout the fabric and especially throughout the yarn bundels. Impregnating fabrics of orientated UHMWPE achieve good impregnation at high fiber content and thus good mechanical properties at low aerial density.

(17) Comparative Experiment E

(18) A flexible tarpaulin sheet made from the same Dyneema® fabric as used in Example 7, but employing a melt impregnation process method as described in WO201104321. The fibre to polyolefin ratio of the sheet was 0.37 (27 wt % fibers). A cross-sectional inspection of the impregnated fabric E showed substantial amount of voids and inhomogeneous impregnation of the fabric.

EXAMPLE 8

(19) Flexible fibrous armor sheet material was made by impregnating a unidirectional layer of Dyneema® 1760 SK76 fibers with a 1:1 dilution of suspension 1 with water. After drying the aerial density of the unidirectional layer was 33 g/m.sup.2 with a fiber to resin ratio of 82:18. The unidirectional layers were cross plied in a 0° 90° 0° 90° sequence, sandwiched between two low density polyethylene foils with a thickness of 7 micrometer and compression molded for 2 minutes at a pressure of 30 bar and a temperature of 115° C. Flexible sheet for soft ballistic applications with an areal density of 146 g/m.sup.2 were obtained.

(20) The flexible sheets were stacked to form a soft ballistic armour which was compared to similar ballistic armour but using commercially available Dyneema® SB21 armour sheets having a built up comparable to the ones according to the invention with the difference that the matrix is a non-crystalline styrenic rubber system (Comparative Experiment F).

(21) The ballistic performance of the stacks build from the sheets of Example 8 and Comparative F proved to be equivalent. Nevertheless peel tests showed that the peeling strength of the sheets according to example 8 are substantially higher than those of SB21. Moreover, the inventive sheets of example 8 had lower scatter (standard deviation) of the peeling strength. That means that the risk of local low bonding and delamination is lower for the sheets according to the invention. Peel tests are performed by peeling upper and lower layers apart, such that the 2.sup.nd and 3.sup.rd layer are separated. The results of the peeling tests are below.

(22) TABLE-US-00004 SB21 Example 8 (reference) Average Peel strength [N] 4.46 4.00 Standard deviation [N] 1.1 2.07

EXAMPLE 9

(23) A fibrous armor sheet material was made by impregnating a unidirectional layer of Dyneema® 880 SK99 fibers with suspension 2. After drying the aerial density of the unidirectional layer was 33 g/m.sup.2 with a fiber to resin ratio of 83:17. Two of such unidirectional layers were stacked in a 0° 90° sequence and laminated. Thus resulting in a cross ply laminate with an aerial density of 66 g/m.sup.2. The sheets were reasonably robust and allowed easy handling and stacking for producing hard ballistic armor plates.

(24) Armor plates were produced by stacking above cross plies in such a way that always 0° 90° sequences occurred. The stacks were made to a total aerial density of 14 kg/m.sup.2 These stacks were pressed at 165 Bar, at a temperature of 135° C. during 30 minutes. Subsequently they were cooled under pressure to 80° C. before the press was opened. The obtained panels were cut to pieces of 0.2 m×0.2 m.

(25) The specimens of 0.2 m×0.2 m were subjected to ballistic testing, by putting them in front of a hard steel plate with a thickness of 7 mm having a central hole with a diameter of 0.14 m. Subsequently. The specimens were shot with a Nato Ball DM111 (obtained from Metallwerk Elisenhütte GmbH, Article number 231007) projectile at a speed of 840 m/sec. All projectiles were stopped. The deformation of the specimens were measured using a high speed camera at the back side where the armor was allowed to deform through the hole in the steel plate. Additionally, the final displacement were measured after the tests.

(26) Comparative Experiment F and G

(27) The process of Example 9 was repeated with the sole difference that the unidirectional layers have been treated with two commercial coatings comprising as a resin PUR and SEBS for Comparative Experiment F and G respectively.

(28) The results are summarized below. For example 9, and Comp Exp. G several specimen were tested and are reported separately. Beside the improved test results it was observed that the panels produced with sheets according to the invention showed no delamination of the unperforated sheets, whereas several panels of the comparative examples F and G delaminated and sheet edges were often pushed through the hole of the steel plate.

(29) TABLE-US-00005 Dynamic displacement Final displacement Material [mm] [mm] Example 9 41 − 33 − 47-37 33 − 27 − 38-31 Comp Experiment F >100 >100 Comp Experiment G 75 − 79 − 62- >100 62 − 73 − 55- >100