FIBROUS TAPE

Abstract

The invention relates to a fibrous tape made from fibers comprising highly oriented polymer, the tape having a tenacity of at least 1.2 N/tex and an areal density of between 5 and 250 g/m.sup.2, wherein the tape has a transversal strength of at least 0.5 MPa. The invention also relates to sheets comprising the tape of the invention and antiballistic articles comprising at least two of said sheets. The invention further relates to a process for the preparation of the tapes of the invention.

Claims

1. A fibrous tape made from fibers comprising highly oriented polymer, the tape having a tenacity of at least 1.2 N/tex and an areal density of between 5 and 250 g/m.sup.2, wherein the tape has a transversal strength of at least 0.5 MPa.

2. The tape of claim 1, wherein the polymer is a polyolefin, preferably a polyethylene and more preferably a high or ultrahigh molecular weight polyethylene (UHMWPE).

3. The tape of claim 1 wherein the tape has a cross-sectional aspect ratio thickness to width of at most 1:50, preferably at most 1:100, more preferably at most 1:500.

4. The tape of claim 1 wherein the tape has a tenacity of at least 1.5 N/tex, preferably at least 2.0 N/tex, more preferably at least 2.5 N/tex, even more preferably 3.0 N/tex and most preferably 3.5 N/tex.

5. The tape of claim 1 wherein the transversal strength is at least 0.6 MPa, more preferably at least 0.7 MPa, even more preferably at least 0.8 MPa, and most preferably at least 0.9 MPa.

6. The tape of claim 1 wherein the fibers comprising the polymer comprise at least 10 ppm of a solvent for the polymer.

7. A sheet comprising at least two monolayers comprising fibrous tape or at least one layer of woven fibrous tapes, wherein the fibrous tapes are selected from claim 1.

8. The sheet according to claim 7 wherein the direction of the fibrous tape in a monolayer is at an angle to the direction of a fibrous tape in an adjacent monolayer or wherein the layer of woven fibrous tapes comprises weft and warp woven tapes and the direction of orientation of the weft and the warp woven tapes in the layer of woven fibrous tapes are at an angle and wherein or are between 20 and 90, more preferably between 45 and 90, most preferably between 75 and 90.

9. An antiballistic article comprising at least 2, preferably at least 4, more preferably at least 8 sheets according to claim 7.

10. The antiballistic article of claim 9 having an areal density between 0.25 Kg/m.sup.2 and 250 Kg/m.sup.2, preferably between 0.5 Kg/m.sup.2 and 100 Kg/m.sup.2, more preferably between 1 Kg/m.sup.2 and 75 kg/m.sup.2 and most preferably between 2 Kg/m.sup.2 and 50 kg/m.sup.2.

11. The antiballistic article of claim 9, comprising a number of contacts between two tapes separated by an intermediate tape, wherein the number of contacts is less than 20 per unit of width of 1 meter of the intermediate tape, while a contact corresponds to a tape-to-tape interaction of the two tapes separated by an intermediate tape, occurring through a split of the intermediate tape.

12. A process for the preparation of the fibrous tape of claim 1, the process comprising: (a) providing fibers comprising a highly oriented polymer, said fibers having a tenacity of at least 1.2 N/tex (b) forming a layer comprising the fibers; (c) applying a longitudinal tensile force to the fibers in the layer, (d) stretching the fiber layer at a draw ratio of at least 1.01 to form a stretched layer; (e) providing the stretched layer at a processing temperature T.sub.p to compression means; (f) compressing the stretched layer of fibers by subjecting the layer to a compression by the compression means having a temperature T.sub.c to form a fibrous tape; (g) optionally stretching the fibrous tape by a draw rate of at most 1.1 and, (h) cooling the fibrous tape to a temperature of at most 80 C. under a tension sufficient to prevent loss of mechanical properties; wherein T.sub.m is the melting temperature of the polymer, wherein T.sub.m>T.sub.pT.sub.m30 K, and wherein T.sub.cT.sub.p3 K.

13. The process according to claim 11 wherein T.sub.m>T.sub.pT.sub.m15 K, and wherein T.sub.cT.sub.p15 K.

14. The process according to claim 11 wherein the polymer is UHMWPE, preferably the UHMWPE has an intrinsic viscosity of between 5 dL/g to 40 dL/g, more preferably between 8 and 30 dL/g.

15. The process of claim 11 wherein the filaments are stretched in between the steps (a) and (f) to a draw ratio from 1.02 to 3.0, preferably 1.03 to 2.0.

Description

[0062] FIGS. 1 and 2 show a light microscopy picture at 2 different scales showing a portion of a cross-section (1) through a panel comprising monolayers the fibrous tapes according to the invention. The monolayers of which the fibers run substantially in parallel to the cross section are of a lighter shade (3 and 4) than the monolayers of which the fibers run substantially perpendicular to the cross-section (2). The position (5) in the figures indicates a split of the tape of monolayer (2), which split has been filled with the tapes of the respective adjacent monolayers (3) and (4).

[0063] The invention will be further explained with the help of the following examples without however being limited thereto.

EXPERIMENTAL

Methods of Measuring

[0064] Areal density (AD) of a panel or sheet was determined by measuring the weight of a sample of preferably 0.4 m0.4 m with an error of 0.1 g. The areal density of a tape was determined by measuring the weight of a sample of preferably 1.0 m0.03 m with an error of 0.1 g. [0065] Intrinsic Viscosity (IV) is determined according to ASTM-D1601/2004 at 135 C. in decalin, the dissolution time being 16 hours, with DBPC as anti-oxidant in an amount of 2 g/l solution, by extrapolating the viscosity as measured at different concentrations to zero concentration. There are several empirical relations between IV and Mw, but such relation is highly dependent on molar mass distribution. Based on the equation M.sub.w=5.37*10.sup.4 [IV].sup.1.37 (see EP 0504954 A1) an IV of 4.5 dl/g would be equivalent to a M.sub.w of about 422 kg/mol. [0066] Side chains in a polyethylene or UHMWPE sample is determined by FTIR on a 2 mm thick compression molded film by quantifying the absorption at 1375 cm.sup.1 using a calibration curve based on NMR measurements (as in e.g. EP 0 269 151) [0067] Tensile properties, i.e. strength and modulus, of fibers were determined on multifilament yarns as specified in 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. For calculation of the strength, the tensile forces measured are divided by the titre, as determined by weighing 10 meter of fibre; values in GPa for are calculated assuming the natural density of the polymer (), e.g. for UHMWPE is 0.97 g/cm.sup.3. [0068] The tensile properties of tapes and films are determined accordingly on tapes of a width of 2 mm twisted 40 turns per meter. [0069] The transversal strength of tapes is measured on a Zwick Z005 tensile tester with a 1 kN force cell and manual G13T and G13B tape clamps. The test samples are prepared by manually cutting the tapes to 250 mm strips. During preparation of the test samples care should be paid to avoid unintentional partial splitting of the tape. Samples which prove impossible to be cut into coherent 250 mm strips are assigned a transverse strength of 0 MPa. The clamping length of the samples is 60 mm and distance between clamps is 20 mm. Pre-load is 0.1 N, and test occurs at a speed of 50 mm/min. The maximum force determines the transversal strength. The strength in MPa is calculated by dividing that maximum force in Newton by the width and the thickness of the sample in mm. Thus a breaking stress in N/mm.sup.2 is achieved, being identical to breaking stress in MPa. The average of 5 samples is reported. [0070] The melting temperature (T.sub.m) of a filament is determined by DSC on a power-compensation Perkin Elmer DSC-7 instrument which is calibrated with indium and tin with a heating rate of 10 K/min on a 5 mg sample. For calibration (two point temperature calibration) of the DSC-7 instrument about 5 mg of indium and about 5 mg of tin are used, both weighed in at least two decimal places. Indium is used for both temperature and heat flow calibration; tin is used for temperature calibration only. [0071] Ballistic performance was measured by subjecting the panels to shooting tests performed with the further indicated ammunition. The first shot was fired at a projectile speed (V.sub.50) at which it is anticipated that 50% of the shots would be stopped. The actual bullet speed was measured at a short distance before impact. If a stop was obtained, the next shot was fired at an anticipated speed being 10% higher than the previous speed. If a perforation occurred, the next shot was fired at an anticipated speed 10% lower than the previous speed. The result for the experimentally obtained V50 value was the average of the two highest stops and the two lowest perforations. The kinetic energy of the bullet at V.sub.50 (E.sub.kin=.Math.m.Math.V.sub.50.sup.2) wherein m is the mass of the projectile, was divided by the areal density of the armor to obtain a so-called E.sub.abs value. E.sub.abs reflects the stopping power of the armor relative to its weight/thickness thereof. The higher the E.sub.abs the better the armor is. [0072] The speed of the projectile was measured with a pair of Drello Infrared (IR) light screen Type LS19i3 positioned perpendicular on the path of the projectile. At the instant when a projectile passes through the first light screen a first electric pulse will be produced due to the disturbance of the IR beam. A second electric pulse will be produced when the projectile passes through the second light screen. Recording the moments in time when the first and the second electric pulses occur, and knowing the distance between the light screed the speed of the projectile can be immediately determined. [0073] Tape-to-tape contacts in a panel are determined by light microscopy of polished cross-sections of a panel. The number of contacts is counted on a cross-section of at least 1 by 5 mm.sup.2. The total width of cross-sectioned tape (in m) present in said cross-section of 1 by 5 mm.sup.2 is calculated multiplying 0.005 m cross-section length by the number of visible cross-sectioned tape, i.e. by dividing the height by the tape thickness.

General Experimental Setup

[0074] 8 multifilament UHMWPE yarns were spread to form a homogeneous layer of filaments with a total thickness of about 50 micron and a width of approximately 3 cm. The filament layer was run through a set of two counter rotating calender rolls of a diameter of 40 cm and a width of 4 cm each. The temperature controlled rolls were set at a speed of 530 cm/min and applied a pressure of 1750 N/mm to the filament layer. A further roller stand placed after the calender rolls applied a tensile force of about 80 N to the tape exiting the nip of the calender rolls and optionally perform a post draw to the formed fibrous tape before being air cooled to a temperature below 80 C. and wound on a bobbin.

Comparative Experiment A

[0075] A multifilament UHMWPE yarn with a tenacity of 3.1 N/tex and a paraffinic solvent level of about 50 ppm was subjected to above general experimental setup. The calender rolls were heated to 161 C. The obtained fibrous tape A had an average thickness of 47.2 micrometer, a width of 28 mm, a titre of 957 dtex and a tenacity of 3.01 N/tex. The transversal strength of the tape was 0.39 MPa.

Comparative Experiment B

[0076] Comparative Experiment A was repeated with the difference that a forced air convection oven at a temperature of 143 C. in between two roller stands applying an tensile force to the filaments was placed before the calender rolls. The tensile force was adjusted to apply a draw rate of 1.12 to the filament layer before entering the calender rolls set at a temperature of 160 C. The obtained fibrous tape B had an average thickness of 47 micrometer, a width of 29 mm, a titre of 968 dtex and a tenacity of 2.83 N/tex. The transversal strength of the tape was 0.41 MPa.

Example 1

[0077] Comparative Experiment B was repeated with the addition that the drawn filament layer was passed over a heated surface of 157 C., the contact path with the heated surface having a length of about 3 cm before entering the calendering rolls set at a temperature of 139 C. The obtained fibrous tape 1 had an average thickness of 39.6 micrometer, a width of 30 mm, a titre of 751 dtex and a tenacity of 3.19 N/tex. The transversal strength of the tape was 0.60 MPa representing about a 50% improvement over the transversal strength of tape B.