Transparent antiballistic article and method for its preparation

Abstract

This invention relates to a process for the preparation of an antiballistic article, the method comprising: a) Providing a transparent uniaxially stretched polymeric film with at least one layer I comprising a semi-crystalline thermoplastic polymer A and at least one layer II comprising an amorphous or semi-crystalline thermoplastic polymer B, of which polymer B has a glass transition temperature less than the melting temperature of polymer A if polymer B is amorphous or of which polymer B has a melting temperature less than the melting temperature of polymer A if polymer B is semi-crystalline; b) Stacking at least two of the uniaxially stretched polymeric films of a) at an angle a of between 45° and 135°, such that the films are in contact with each subsequent film through at least one layer II, to form an assembly; c) Compressing the thus formed assembly at a temperature above the glass transition temperature of polymer B if polymer B is amorphous, or above the melting temperature of polymer B if polymer B is semi-crystalline, and below the melting temperature of polymer A, to obtain an haze of at most 50% and having an energy absorption for 17 grain FSP according to the STANAG 2920 standard of at least 12 J/(kg/m.sup.2). The invention also relates to antiballistic articles.

Claims

1. A method for the preparation of an antiballistic article, the method comprising the steps of: (a) providing a transparent uniaxially stretched polymeric film with at least one layer I comprising a semi-crystalline thermoplastic polymer A and at least one layer II comprising an amorphous or semi-crystalline thermoplastic polymer B, wherein the polymer B has a glass transition temperature which is at least 15° C. less than a melting temperature of the polymer A if the polymer B is amorphous or wherein the polymer B has a melting temperature which is at least 15° C. less than the melting temperature of the polymer A if the polymer B is semi-crystalline; (b) stacking at least two of the uniaxially stretched polymeric films of step (a) at an angle α of between 45° and 135° , such that the films are in contact with each subsequent film through at least one layer II, to form an assembly; (c) compressing the thus formed assembly of step (b) at a temperature above the glass transition temperature of polymer B if polymer B is amorphous, or above the melting temperature of polymer B if polymer B is semi-crystalline, and below the melting temperature of polymer A, to obtain a haze of at most 50% and having an energy absorption for 17 grain FSP according to the STANAG 2920 standard of at least 12 J/(kg/m.sup.2).

2. The method according to claim 1, wherein the haze is at most 10%.

3. The method according to claim 1, wherein the angle α is between 80° and 100° .

4. The method according to claim 1, wherein the uniaxially stretched polymeric film in step (a) has a total of 3 layers, wherein two layers II are opposite of one layer I.

5. The method according to claim 1, wherein step (b) includes contacting the films with each subsequent film through two layers II.

6. The method according to claim 4, wherein the polymer B in the two layers II is the same.

7. The method according to claim 1, wherein the polymer A is selected from the group consisting of polyamides, co-polyamides, polyesters, and polypropylene.

8. The method according to claim 1, wherein the polymer A is selected from the group consisting of aliphatic polyamides, semi-aromatic polyamides, and polyamide blends.

9. The method according to claim 1, wherein the polymer B is a co-polyamide.

10. The method according to claim 1, wherein the polymer A is polyamide-6/6T and the polymer B is a polyamide-6/66.

11. The method according to claim 1, wherein step c) is performed by compressing the assembly at a pressure less than 100 Bar.

12. The method according to claim 1, wherein step (c) is performed by compressing the assembly at a pressure less than 50 Bar.

13. The method according to claim 1, wherein the uniaxially stretched polymeric film provided in step (a) is prepared by a multilayer film cast extrusion process.

14. The method according to claim 1, wherein the polymer B has a glass transition temperature which is at least 20° C. less that the melting temperature of the polymer A if the polymer B is amorphous or wherein the polymer B has a melting temperature which is at least 20° C. less than the melting temperature of the polymer A if the polymer B is semi-crystalline.

15. The method according to claim 1, wherein the polymer B has a glass transition temperature which is at least 30° C. less that the melting temperature of the polymer A if the polymer B is amorphous or wherein the polymer B has a melting temperature which is at least 30° C. less than the melting temperature of the polymer A if the polymer B is semi-crystalline.

16. An antiballistic article obtained by the method of claim 1 having a haze of at most 10% and having an energy absorption for 17 grain FSP according to the STANAG 2920 standard of at least 12 J/(kg/m.sup.2).

Description

EXAMPLES

Example 1

(1) This example deals with a three layer polyamide film consisting of one layer I of polymer A being PA6/6T, which is a PA6 based copolymer with 10%6T, and two layers II on both sides consisting of polymer B being PA6/66 with 20% 66. This film was produced by multilayer film cast extrusion process. A single screw extruder (screw diameter 30 mm, L/D=30) and a single screw extruder (screw diameter 25 mm, L/D=25) were connected to a feed block with a slot die with adjustable die-lip. The 30 mm extruder was fed with layer I material; barrel temperature set to 260° C., throughput 12 kg/h., screw speed 120 rpm. The 25 mm extruder was fed with layer II material; barrel temperature 230° C., throughput 1.0 kg/h, screw speed 100 rpm. Standard transport screws were used. The die-width was 300 mm and the die-width was 0.8 mm. The film was cooled on a chill role. The thickness of the film was regulated by the drawdown ratio and for this example was 123 μm. The chill role temperature was 23° C. and to obtain good contact between melt and chill role air pinning was applied. The film was in line trimmed to a width of 75 mm. During experimentation, measures were taken to prevent moisture uptake of the films as much as possible.

(2) The cast film was uniaxially stretched. The stretching process occurred by leading the film over various metal roller sets. The film entered the roller set with an initial speed of 3 m/min and was heated by the rolls to 80° C. A first stretching step was performed by variation of the speed of uptake rolls. The maximum degree of stretching in this first stretching step was 3.0. A second stretching step was performed at 180° C. The maximum degree of stretching in this step was 2.7. The haze of the film after the second stretching step was 7%. After the second stretching step the film was heat set by leading the film over a role at 180° C.

(3) Based on this film, ballistic objects were made out of many polymeric stretched films that were stacked with an angle α of 90° (cross plied). Several film materials were stacked in a 70×70 mm mold and consolidated. To prevent air inclusion between the individual layers, the stacked objects were packed in a seal bag made of similar material and brought to vacuum conditions. Compression was performed at 191° C. at a pressure of 10 bar (equivalent to 1 MPa=1.000 kN/m2) applied by a parallel plate press. Good adhesion was observed. After compression, the layers could not be separated by hand.

Example 2

(4) This example deals with a three layer polyamide film consisting of one layer I of polymer A being PA6/6T, which is a PA6 based copolymer with 10% 6T, and two layers II on both sides consisting of polymer B being PA6I/6T with 66% 6T, an amorphous polyamide. This film was produced by multilayer film cast extrusion process. A single screw extruder (screw diameter 30 mm, L/D=30) and a single screw extruder (screw diameter 25 mm, L/D=25) were connected to a feed block with a slot die with adjustable die-lip. The 30 mm extruder was fed with layer I material; barrel temperature set to 260° C., throughput 12 kg/h., screw speed 120 rpm. The 25 mm extruder was fed with layer II material; barrel temperature 230° C., throughput 1.0 kg/h, screw speed 100 rpm. Standard transport screws were used. The die-width was 300 mm and the die-width was 0.8 mm. The film was cooled on a chill role. The thickness of the film was regulated by the drawdown ratio and for this example was 121 μm. The chill role temperature was 23° C. and to obtain good contact between melt and chill role air pinning was applied. The film was in line trimmed to a width of 75 mm. During experimentation, measures were taken to prevent moisture uptake of the films as much as possible.

(5) The cast film was uniaxially stretched. The stretching process occurred by leading the film over various metal roller sets. The film entered the roller set with an initial speed of 3 m/min and was heated by the rolls to 80° C. A first stretching step was performed by variation of the speed of uptake rolls. The maximum degree of stretching in this first stretching step was 3.1. A second stretching step was performed at 120° C. The maximum degree of stretching in this step was 2.2. The haze of the film after the second stretching step was 4%. After the second stretching step the film was heat set by leading the film over a role at 120° C.

(6) Based on this film, ballistic objects were made out of many polymeric stretched films that were stacked with an angle α of 90° (cross plied). Several film materials were stacked in a 70×70 mm mold and consolidate. To prevent air inclusion between the individual layers, the stacked objects were packed in a seal bag made of similar material and brought to vacuum conditions. Compression was performed at 160° C. at a pressure of 10 bar (equivalent to1 MPa=1.000 kN/m2) applied by a parallel plate press. Good adhesion was observed. After compression, the layers could not be separated by hand.

Example 3

(7) This example deals with a three layer polyamide film consisting of a layer I of polymer A being film grade polyamide-6 with a relative solution viscosity of 3.2 as measured in formic acid of 90% at a concentration of 0.01 g/ml at 25° C. and on both sides a layer II consisting of a polymer B being copolyamide PA6/66 with 20% 66. This film was produced by a multilayer film cast process as described before. All conditions were identical to example 2 except for the barrel temperature of the 25 mm extruder for polymer B; it was set to 250° C. Film thickness was 118 μm. This film was uniaxially stretched according to the procedure of example 2. First stretching step was performed at 70° C.; and the maximum degree of stretching amounted to 3.0. A second stretching step was performed 180° C. The maximum degree of stretching in this step was 2.4. After the second stretching step the film was heat set by leading the film over a role at 180° C.

(8) Based on this film, ballistic objects are made out of many individual polymeric stretched films that were stacked with an angle α of 90° (cross plied). Several film materials were stacked in a 70×70 mm mold and consolidate. To prevent air inclusion between the individual layers, the stacked objects were packed in a seal bag made of similar material and brought to vacuum conditions. Compression was performed at 191° C. at a pressure of 10 bar (equivalent to 1 MPa=1.000 kN/m2) applied by a parallel plate press. Good adhesion was observed. After compression, the layers could not be separated by hand.

Comparative Example 1

(9) The transparent benchmark was obtained from Cleargard (Ballistic Polycarbonate sheet) the material consisted of two fused sheets with an individual thickness of 2.5 mm, a surface density of 5.5 kg/m.sup.2, a tensile strength of 70 MPa and a E-modulus of 2 GPa.

Comparative Examples 2 and 3

(10) UHMWPE gel film with a width of ±71 mm was received from DSM Solutech (P091012A-D01-A). The film was produced from a 10% UHMWPE (FG113) solution in decaline and uni-axial drawn with an unspecified draw ratio, a surface density of 17.8 gr/m.sup.2. The thickness over the width of the film was not uniform, the edges had a thickness of 26 μm and the centre of the film was 17 μm. The maximal tensile strength was 16.2 cN/dtex and the E-modulus was 100 GPa.

(11) Ballistic objects were made out of many individual films that were with an angle α of 90° (cross plied). Several film and yarn materials were stacked in a 70×70 mm mold and consolidated at temperature just below the melting point of 145C to keep all mechanical properties untouched and to induce a kind of fusing the individual layers together to result in a solid sheet.

(12) To overcome air inclusion in the pressed sheets, the pressing was performed under vacuum in a vacuum chamber press. The fusing procedure for the UHMWPE materials needed high pressures (>800 bar=80 MPa=80.000 kN/m.sup.2) applied by a parallel plate press to realize a more or less solid (cohesive) sheet. The by this fusing procedure obtained consolidated sheet showed a low level of adhesion between the individual layers. Pushing a sharp object in the side of the sheet resulted in delamination.

Comparative Example 4

(13) This example deals with a single layer polyamide film consisting of a film grade PA6 with a relative viscosity of 3.2, as measured in formic acid of 90% at a concentration of 0.01g/ml at 25° C. This film was produced by a film cast process as described before. Only one extruder (30 mm) was connected to the feedblock. The extruder was operated at a barrel temperature 260° C., throughput 13 kg/h. Film thickness was 120 μm. This film was uniaxially stretched according to the procedure of example 1. First stretching step was performed at 70° C. with a maximum degree of stretching of 2.9. A second stretching step was performed 130° C. The maximum degree of stretching in this step was 1.7. After the second stretching step the film was heat set by leading the film over a role at 190° C.

(14) This film was used to create a multistacking as described before. The fusing procedure for the PA6 uniaxial drawn material needed much higher pressures (>800 bar=80 MPa=80.000 kN/m.sup.2) applied by a parallel plate press compared to examples 6 and 7 to realize a solid (cohesive) sheet. The by this fusing procedure obtained consolidated sheet exhibited a low level of adhesion between the individual layers. Pushing a sharp object in the side of the sheet resulted in delamination.

Comparative Example 5

(15) A biaxially oriented (BOPA) film from polyamide-6 had a degree of stretching of 3×3 and was obtained from DSM Akulon. The film had a surface density of 15 gr/m.sup.2 and a homogeneous thickness of 13 μm. The maximal tensile strength in the machine direction was 160 MPa, a E-modulus of 1 GPa and in the transversal direction the tensile strength was 110 MPa with a E-modulus of 1 GPa.

(16) To overcome air inclusion in the pressed sheets, the pressing was performed under vacuum in a vacuum chamber press. The fusing procedure for BOPA needed high pressures (>800 bar=80 MPa=80.000 kN/m.sup.2) applied by a parallel plate press to realize a solid (cohesive) sheet. The by this fusing procedure obtained consolidated sheet exhibited a low level of adhesion between the individual layers. Pushing a sharp object in the side of the sheet resulted in delamination.

Comparative Example 6

(17) Biaxially oriented polypropylene film (BoPP) with a layer I of polymer A being polypropylene and as surface layers two layers II of a polymer B being a heat sealable layer, as commercially available from ExxonMobil called Bicor 30MB400. The sealable layer of the BOPP was not investigated but the technical data sheet mentioned a melting point (seal temperature) of ˜130° C. Since PP has a melting point of ˜160° C. the mechanical properties of the layer I material PP stayed untouched during compression at 130° C. The individual stacked films were compressed with very low pressures 10 bar (equivalent to 1 MPa=1.000 kN/m2), applied by a parallel plate press to create a solid sheet with good adhesion. After compression the layers could not be separated by hand.

(18) Performance Testing of Articles

(19) The articles were subjected to shooting tests performed with 17 grain FSP. The tests were performed with the aim of determining the energy absorbed (E-abs) at V50. V50 is the speed at which 50% of the projectiles will penetrate the armoured plate. The testing procedure was as follows. The first projectile was fired at the anticipated V50 speed. The actual speed was measured shortly before impact. If the projectile was stopped, a next projectile was fired at an intended speed of about 10% higher. If it perforated, the next projectile was fires at an intended speed of about 10% lower. The actual speed of impact was always measured. V50 was the average of the two highest stops and the two lowest perforations. The performance of the armour was also determined by calculating the kinetic energy of the projectile at V50 and dividing this by the areal density (AD) of the plate (E-abs).

(20) Optical Testing of Articles

(21) The produced articles were subject to a haze measurement according to ASTM D-1003, measured at a sample thickness of 2 mm and at a wavelength of 600 nm. In this application optical transparency is defined by haze in percentages according to the ASTM D-1003 method.

(22) Tensile strength was measured according to ASTM D882-88, method A: 500 mm/min.

(23) T.sub.g and T.sub.m and tensile strengths were measured of the films used in the process according to the invention and listed in Table 1.

(24) TABLE-US-00001 TABLE 1 Tg and Tm and tensile strength values of the examples according to the invention T.sub.g & T.sub.m Tensile strength Example Material [° C.] MPa 1 Uniaxial stretched: 57 & 205 MD: 507 Polymer A PA6/6T 50 & 190 TD: 55.6 Polymer B PA6/66 2 Uniaxial stretched: 57 & 205 Polymer A PA6/6T; Tg = 127 Polymer B PA6I/6T 3 Uniaxial stretched; 60 & 225 MD: 295 Polymer A PA6 50 & 190 TD: 72 Polymer B PA6/66 MD: machine direction, thus in strongest direction; TD transverse direction

(25) TABLE-US-00002 TABLE 2 Results Haze [%] Sheet @ 600 nm; Energy consolidation @2 mm absorbed FSP Example Material pressure [Bar] thickness [J/(kg/m2)] 1 Uniaxial stretched: 10 15 18 Polymer A PA6/6T; Polymer B PA6/66 2 Uniaxial stretched: 10 4 15 Polymer A PA6/6T; Polymer B PA6I/6T 3 Uniaxial stretched; 10 7 16 Polymer A PA6 Polymer B PA6/66 Comparative 1 Polycarbonate Not applicable 3 8 Comparative 2 UHMWPE Gel film; 800 55 50 fully stretched Comparative 3 UHMWPE Gel film; 800 45 34 partially stretched Comparative 4 Uniaxial PA6 800 8 15 Comparative 5 Biaxially stretched 800 — 8 polyamide Comparative 6 Biaxially stretched 10 5 10 Layer I polypropylene Layer II PE

(26) The results in Table 2 clearly show that with a process according to the invention antiballistic articles can be obtained with a very low haze, while have an energy absorbed FSP of at least 12 J(kg/m2). When biaxially stretched films were used, much less energy could be absorbed, which is indicative for a low ballistic performance. If the films did not comprise a layer I and a layer II, such as in comparative examples 2 to 5, it becomes clear that high pressures were needed to obtain sheet consolidation.