HIGH PERFORMANCE FIBERS COMPOSITE SHEET

Abstract

Composite sheets include at least two adjacent fibrous monolayers of unidirectionally aligned high tenacity polyethylene fibers, whereby the direction of orientation between the polyethylene fibers of said two fibrous layers differs by at least 80° and up to 90°, the fibers having a tenacity of at least 1.5 N/tex, the fibers being in a matrix comprising a homopolymer or copolymer of ethylene and wherein the homopolymer or copolymer of ethylene has a density as measured according to ISO1183 of between 870 to 980 kg/m.sup.3. The composite sheets have an areal density of between 50 and 500 g/m.sup.2, wherein the composite sheets have an areal density normalized in-plane shear force measured at 25° C. evaluated according to a bias extension test method variant of ASTM D3518 of at least 0.40 N.Math.m.sup.2.Math.g.sup.−1 and lower than 5.0 N.Math.m.sup.2.Math.g.sup.−1 at 10 mm clamp displacement and an areal density normalized in-plane shear force measured at 110° C. and clamp displacement of 10 mm of at least 0.01 N.Math.m.sup.2.Math.g.sup.−1 and lower than 0.20 N.Math.m.sup.2.Math.g.sup.−1.

Claims

1. A composite sheet comprising: a matrix comprising a homopolymer or copolymer of ethylene having a density as measured according to ISO1183 of between 870 to 980 kg/m.sup.3, and at least two adjacent fibrous monolayers of unidirectionally aligned high tenacity polyethylene fibers impregnated with the matrix, wherein a direction of orientation between the polyethylene fibers of the at least two fibrous layers differs by at least 80° and up to 90°, wherein the fibers have a tenacity of at least 1.5 N/tex, and wherein the composite sheet has an areal density of between 50 and 500 g/m.sup.2 wherein the composite sheet has an areal density normalized in-plane shear force measured at 25° C. evaluated according to a bias extension test method variant of ASTM D3518 of at least 0.40 N.Math.m.sup.2.Math.g.sup.−1 and lower than 5.0 N.Math.m.sup.2.Math.g.sup.−1 at 10 mm clamp displacement and an areal density normalized in-plane shear force measured at 110° C. and clamp displacement of 10 mm of at least 0.01 N.Math.m.sup.2.Math.g.sup.−1 and lower than 0.20 N.Math.m.sup.2.Math.g.sup.−1.

2. The composite sheet according to claim 1, wherein the areal density normalized in-plane shear force measured at 25° C. of the composite sheet is at least 0.50 N.Math.m.sup.2.Math.g.sup.−1 and lower than 3.0 N.Math.m.sup.2.Math.g.sup.−1.

3. The composite sheet according to claim 1, wherein the areal density normalized in-plane shear force measured at 25° C. of the composite sheet is at least 0.60 N.Math.m.sup.2.Math.g.sup.−1 and lower than 2.0 N.Math.m.sup.2.Math.g.sup.−1.

4. The composite sheet according to claim 1, wherein the areal density normalized in-plane shear force measured at 25° C. of the composite sheet is at least 0.70 N.Math.m.sup.2.Math.g.sup.−1 and lower than 1.5 N.Math.m.sup.2.Math.g.sup.−1.

5. The composite sheet according to claim 1, wherein the areal density normalized in-plane shear force measured at 25° C. of the composite sheet is at least 0.90 N.Math.m.sup.2.Math.g.sup.−1 and lower than 1.5 N.Math.m.sup.2.Math.g.sup.−1.

6. The composite sheet according to claim 1, wherein the areal density normalized in-plane shear force measured at 25° C. of the composite sheet is at least 1.0 N.Math.m.sup.2.Math.g.sup.−1 and lower than 1.5 N.Math.m.sup.2.Math.g.sup.−1.

7. The composite sheet according to claim 1, wherein the areal density normalized in-plane shear force measured at 110° C. of the composite sheet is at least 0.03 N.Math.m.sup.2.Math.g.sup.−1 and lower than 0.10 N.Math.m.sup.2.Math.g.sup.−1.

8. The composite sheet according to claim 1, wherein the areal density normalized in-plane shear force measured at 110° C. of the composite sheet is at least 0.04 N.Math.m.sup.2.Math.g.sup.−1 and lower than 0.08 N.Math.m.sup.2.Math.g.sup.−1.

9. The composite sheet according to claim 1, wherein the areal density normalized in-plane shear force measured at 110° C. of the composite sheet is at least 0.05 N.Math.m.sup.2.Math.g.sup.−1 and lower than 0.06 N.Math.m.sup.2.Math.g.sup.−1.

10. The composite sheet according to claim 1, wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 30 N.Math.m.sup.2.Math.g.sup.−1 and less than 200 N.Math.m.sup.2.Math.g.sup.−1, the in-plane shear secant stiffness being measured at 25° C. according to the bias extension test.

11. The composite sheet according to claim 1, wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 40 N.Math.m.sup.2.Math.g.sup.−1 and less than 150 N.Math.m.sup.2.Math.g.sup.−1, the in-plane shear secant stiffness being measured at 25° C. according to the bias extension test.

12. The composite sheet according to claim 1, wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 50 N.Math.m.sup.2.Math.g.sup.−1 and less than 100 N.Math.m.sup.2.Math.g.sup.−1, the in-plane shear secant stiffness being measured at 25° C. according to the bias extension test.

13. The composite sheet according to claim 1, wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 60 N.Math.m.sup.2.Math.g.sup.−1 and less than 100 N.Math.m.sup.2.Math.g.sup.−1, the in-plane shear secant stiffness being measured at 25° C. according to the bias extension test.

14. The composite sheet according to claim 1, wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 0.5 N.Math.m.sup.2.Math.g.sup.−1 and less than 7.0 N.Math.m.sup.2.Math.g.sup.−1, the in-plane shear secant stiffness being measured at 110° C. according to the bias extension test.

15. The composite sheet according to claim 1, wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 1.0 N.Math.m.sup.2.Math.g.sup.−1 and less than 5.0 N.Math.m.sup.2.Math.g.sup.−1, the in-plane shear secant stiffness being measured at 110° C. according to the bias extension test.

16. The composite sheet according to claim 1, wherein the composite sheet has an areal density normalized in-plane shear secant stiffness at 1% longitudinal deformation of at least 1.5 N.Math.m.sup.2.Math.g.sup.−1 and less than 3.0 N.Math.m.sup.2.Math.g.sup.−1, the in-plane shear secant stiffness being measured at 110° C. according to the bias extension test.

17. The composite sheet of claim 1, comprising from 2 to 25 wt % of the homopolymer or copolymer of ethylene, based on the total weight of the composite sheet.

18. The composite sheet of claim 17, wherein the matrix comprises an ethylene acrylic acid (EAA) copolymer, an ethylene methacrylic acid (EMA) copolymer or mixtures thereof.

19. A ballistic resistant article comprising at least one composite sheet as defined in claim 1.

20. The ballistic resistant article of claim 19, wherein the article is a compression molded panel which comprises at least 10 of the composite sheets.

Description

FIGURES

[0069] FIG. 1 is a schematic representation of the bias extension test setup showing the sample sheet with a width of 100 mm and length 300 mm. The fiber directions run in +/−45° direction relative to the length direction, X. The sample is clamped with a fixed clamp and a moving clamp whereby the free length between the clamps is 200 mm. Upon testing the moving clamp is displaced downwards, in direction of the arrow, elongating the sample. The force to extend this sample in length direction at a clamp speed of 50 mm/min is sampled at a sufficiently high rate. An overlay of typical plots recorded is presented in FIG. 2.

[0070] FIG. 2 is an overlay of bias extension test results measured at 25° C. temperature according to the above described method. The extensional force normalized to the areal density of the samples on the y-axis is plotted in N.Math.m.sup.2.Math.g.sup.−1 against the longitudinal displacement of the test sample in mm. For each of the Examples (EX1 and EX2) and comparative Experiments (CE A and CE B) the plots for 3 individual samples (−1, −2 and −3) are shown.

[0071] FIG. 3 is an overlay of bias extension test results measured at 25° C. temperature according to the above described method. The extensional force normalized to the areal density of the samples on the y-axis is plotted in N.Math.m.sup.2.Math.g.sup.−1 against the longitudinal strain of the test sample in percent elongation. For each of the Examples (EX1 and EX2) and comparative Experiments (CE A and CE B) the plots for 3 individual samples (−1, −2 and −3) are shown.

[0072] FIG. 4 is an overlay of bias extension test results measured at 110° C. temperature according to the above described method. The extensional force normalized to the areal density of the samples on the y-axis is plotted in N.Math.m.sup.2.Math.g.sup.−1 against the longitudinal displacement of the test sample in mm. For each of the Examples (EX1 and EX2) and comparative Experiment (CE B) the plots for 3 individual samples (−1, −2 and −3) are shown.

[0073] FIG. 5 is an overlay of bias extension test results measured at 110° C. temperature according to the above described method. The extensional force normalized to the areal density of the samples on the y-axis is plotted in N.Math.m.sup.2.Math.g.sup.−1 against the longitudinal strain of the test sample in percent elongation. For each of the Examples (EX1 and EX2) and comparative Experiment (CE B) the plots for 3 individual samples (−1, −2 and −3) are shown.

EXPERIMENTAL

Comparative Experiment A

[0074] Monolayers of polyethylene fibers were prepared according to the process as described in WO2005066401. Here for the multifilament yarn Dyneema® 880 SK99 (DSM, The Netherlands) having a titer of 880 dtex and a tenacity of 4.25 N/tex was used to make a uni-directional (UD) mono-layer by feeding the yarn from several packages from a creel, spreading the filaments, and impregnating the filaments with an aqueous dispersion of Kraton® D11 07 stryrene-isoprene-styrene blockcopolymer as matrix material having a modulus by DMTA of 0.9 MPa and <<0.01 MPA at 25° C. and 110° C. respectively. After drying the UD monolayer had an areal density of 34 g/m.sup.2 and a matrix content of about 16 wt %. 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 composite sheet, bare of further protective films, had an areal density of 136 g/m.sup.2.

Comparative Experiment B

[0075] Comparative Experiment A was repeated with the difference that a commercially available polyurethane suspension in water was applied to the monolayers resulting in a composite sheet with a matrix level of about 17% and an areal density of about 138 g/m.sup.2. The dried PUR has a modulus by DMTA of 55 MPa and 4.5 MPA at 25° C. and 110° C. respectively.

Example 1

[0076] Comparative Experiment A was repeated with the difference that a 28 wt % aqueous dispersion of an ethylene acrylic acid copolymer was used to impregnate the monolayers. The copolymer had an acrylic acid content of about 30 wt % and a melt flow index of >200 g/10 min (21.6 kg, 190° C.). The EAA copolymer had a melting peak at 78° C., a heat of fusion of 29 J/g, and a modulus by DMTA of 280 MPa and <<0.01 MPA at 25° C. and 110° C. respectively. A composite sheet with a matrix content of 15 wt % and an areal density of about 134 g/m.sup.2 was obtained.

Example 2

[0077] Comparative Experiment A was repeated with the difference that a 25 wt % aqueous dispersion of a neutralized ethylene acrylic acid copolymer was used. The acrylic acid level of the copolymer was about 10 wt % whereby the neutralization of the carboxylic acid exceeded 98% and consisted of about 17 mol % ammonia and 83 mol % potassium counter ions. The melt flow index of the dried neutralized copolymer was 4.5 g/10 min (21.6 kg, 190° C.). The neutralized copolymer had a peak melting temperature at 85° C. a modulus by DMTA of 150 MPa and 0.7 MPA at 25° C. and 110° C. respectively. A composite sheet with a matrix content of about 13 wt % and an areal density of about 126 g/m.sup.2 was obtained.

[0078] Rectangular samples (10 cm×30 cm) of all above composite sheets where cut with the fiber orientation in the −45/+45° direction of said rectangular samples. The samples were tested for in-plane shear properties according to ASTM D3518-94. The respective data are reported in Table 1.

TABLE-US-00001 TABLE 1 Norm. Norm. Norm. Norm. force, force, Secant Secant 25° C. @ 110° C. @ stiffness, stiffness, 10 mm 10 mm 25° C. @ 110° C. @ AD displ. displ. 1% deform. 1% deform. Example Matrix [g/m.sup.2] [N .Math. m.sup.2 .Math. g.sup.−1] [N .Math. m.sup.2 .Math. g.sup.−1] [N .Math. m.sup.2 .Math. g.sup.−1] [N .Math. m.sup.2 .Math. g.sup.−1] CE A SEBS 136 0.17 — 9 — CE B PUR 138 0.19 0.054 10 2.31 Ex 1 EAA 134 0.86 0.014 49 0.87 Ex 2 K/NH.sub.4.sup.+- 126 1.15 0.048 72 2.34 ionomer

[0079] Composite sheets (plies) of each of the examples and comparative experiments having a size of 100×100 cm.sup.2 have been assembled to create stack with an areal density of about 15 kg/m.sup.2. These stacks where put in a cold press and pressurized to 165 bar while being heated to 135° C. The core reached the set temperature of 135° C. after 30 minutes compression and was kept for further 5 minutes at 135° C. and 165 bar. The pressure was maintained during cooling until the core temperature reached 60° C. followed by removal of the compressed panel from the press.

[0080] The panels produced from the sheets of comparative experiments A and B both showed blisters on their surface upon removal from the press. The panels comprising the polyethylene resins according to the invention showed a homogeneous surface without any detectable inhomogeneity. Surface and bulk appearance of the panels made with sheets of example 1 and 2 did not change even after 24 h storage at room temperature.