Process for the manufacture of a multilayer material sheet, multilayer material sheet and use hereof

Abstract

Multilayer material sheets containing unidirectional high performance fibers are obtained by a process which includes the steps of positioning the fibers in a parallel fashion, consolidation of the fibers to obtain a monolayer, stacking at least two monolayers such that the fiber direction in one monolayer is at an angle a to the direction of the fibers in an adjacent monolayer and fixation whereby the stack of at least two monolayers is subjected to a pressure and temperature treatment for a duration of a least 2 seconds, followed by cooling the stack under pressure to a temperature of 120 C. or lower. The multilayer material sheet has a reduced uptake of liquids.

Claims

1. A multilayer material sheet suitable for use in soft ballistic applications, wherein the multilayer material sheet comprises: at least two monolayers comprised of unidirectional high performance fibers with a tensile strength of at least 1.0 GPa and a tensile modulus of at least 40 GPa, and at least one plastic film positioned at an outer surface of the multilayer material sheet to allow the multilayer material sheet and an adjacent multilayer material sheet in a stack thereof to slide relative to one another, wherein the multilayer material sheet is obtained by a process comprising the steps of: (a) positioning the fibers in a parallel fashion, (b) consolidating the parallel fibers to obtain a monolayer, (c) stacking at least two monolayers such that a fiber direction in one monolayer is at an angle a relative to a direction of the fibers in an adjacent monolayer to thereby form a continuous stack, and (d) fixating the continuous stack of at least two monolayers formed by step (c) by subjecting the continuous stack of at least two monolayers for a duration of at least 2 seconds to a pressure treatment at a pressure of at least 0.5 MPa and a temperature treatment at a temperature below a melting point or degradation temperature of the fibers to thereby form a pressure and temperature treated stack of at least two fixed monolayers, and thereafter (e) subjecting the pressure and temperature treated stack of at least two fixed monolayers formed by step (d) to controllable rapid cooling under pressure to cool the stack of at least two fixed monolayers from the melting point or degradation temperature of the fibers to a temperature of 80 C. or lower within at least 2 seconds to less than 120 seconds.

2. The multilayer material sheet of claim 1, wherein the unidirectional high performance fibers are polyolefin fibers.

3. The multilayer material sheet of claim 1, wherein the unidirectional high performance fibers are polyethylene fibers.

4. The multilayer material sheet according to claim 3, wherein the polyethylene fibers are ultrahigh molecular weight polyethylene fibers.

5. The multilayer material sheet according to claim 4, wherein the at least one plastic film has a thickness between 1-30 m.

6. The multilayer material sheet of claim 1, wherein the unidirectional high performance fibers are aramid fibers.

7. The multilayer material sheet according to claim 1, which further comprises an elastomeric matrix material having a tensile modulus at 25 C. of at most 41 MPa.

8. The multilayer material sheet according to claim 1, which further comprises a matrix material which includes a polyurethane.

9. The multilayer material sheet according to claim 1, wherein the at least one plastic film has a thickness between 1-30 m.

10. A soft ballistic article comprising the multilayer material sheet according to claim 1.

11. A soft ballistic article comprising a stack of multilayer material sheets, wherein the multilayer material sheets in the stack comprise: at least two monolayers comprised of unidirectional high performance fibers with a tensile strength of at least 1.0 GPa and a tensile modulus of at least 40 GPa, and at least one plastic film positioned at an outer surface of the multilayer material sheets to allow adjacent multilayer material sheets in the stack to slide relative to one another, wherein the multilayer material sheets in the stack are obtained by a process comprising the steps of: (a) positioning the fibers in a parallel fashion, (b) consolidating the parallel fibers to obtain a monolayer, (c) stacking at least two monolayers such that a fiber direction in one monolayer is at an angle a relative to a direction of the fibers in an adjacent monolayer to thereby form a continuous stack, and (d) fixating the continuous stack of at least two monolayers formed by step (c) by subjecting the continuous stack of at least two monolayers for a duration of at least 2 seconds to a pressure treatment at a pressure of at least 0.5 MPa and a temperature treatment at a temperature below a melting point or degradation temperature of the fibers to thereby form a pressure and temperature treated stack of at least two fixed monolayers, and thereafter (e) subjecting the pressure and temperature treated stack of at least two fixed monolayers formed by step (d) to controllable rapid cooling under pressure to cool the stack of at least two fixed monolayers from the melting point or degradation temperature of the fibers to a temperature of 80 C. or lower within at least 2 seconds to less than 120 seconds.

12. The soft ballistic article according to claim 11, wherein the unidirectional high performance fibers are polyolefin fibers.

13. The soft ballistic article according to claim 11, wherein the unidirectional high performance fibers are polyethylene fibers.

14. The soft ballistic article according to claim 11, wherein the unidirectional high performance fibers are aramid fibers.

15. The soft ballistic article according to claim 13, wherein the polyethylene fibers are ultrahigh molecular weight polyethylene fibers.

16. The soft ballistic article according to claim 15, wherein the at least one plastic film has a thickness between 1-30 m.

17. The soft ballistic article according to claim 11, which further comprises an elastomeric matrix material having a tensile modulus at 25 C. of at most 41 MPa.

18. The soft ballistic article according to claim 11, which further comprises a matrix material which includes a polyurethane.

19. The soft ballistic article according to claim 11, wherein the at least one plastic film has a thickness between 1-30 m.

Description

(1) The invention will now be elucidated by the following examples and comparative experiment without being limited hereto.

COMPARATIVE EXPERIMENT A

(2) A multilayer material sheet, comprising ultra high molecular weight polyethylene fibers manufactured by DSM Dyneema with a strength of 3.5 GPa, was made by parallel aligning the fibers and adding 18 wt % of a Kraton styrene-isoprene-styrene triblock copolymer as matrix. Total weight of the monolayer was 65.5 gram. Two of such monolayers were stacked such that the fiber direction between the 2 monolayers was at an angle of 90. At both outer surfaces a LLDPE film with a thickness of 7 micrometer was added and the stack was calendared at a temperature of 135 C. and a line pressure of 45 N/mm to obtain a multilayered material sheet. Pressing time in the calendar was 0.15 second.

(3) From this multilayer material sheet squares of 40*40 cm were cut and immersed in a detergent solution comprising 95 wt % water and 5 wt % of commercially available detergent. Immersion took place during 30 minutes after which the multilayer material sheet was wiped off with paper towel and weight gain (compared to weight before immersion) was recorded.

EXAMPLE 1

(4) The multilayer material sheet comprising ultra high molecular weight polyethylene fibers as made in comparative experiment A was fed through a double belt press at a pressure of 8 MPa and a temperature of 130 C. for a time of 10.5 seconds, followed by cooling under pressure to 80 C. before exiting the double belt press. Samples of 40*40 cm were cut and liquid uptake was determined in the same manner as for comparative experiment A.

COMPARATIVE EXPERIMENT B

(5) A multilayer material sheet comprising cross plied monolayers of unidirectionally aligned aramid fibers, commercially available under the name Gold Flex 95638/AD266, was taken and samples of 40*40 cm were cut. From these samples kerosene uptake was determined by immersion in kerosene during 30 minutes after which the multilayer material sheet was wiped off with paper towel and weight gain (compared to weight before immersion) was recorded. Furthermore the ballistic resistance of a stack, with a total weight of 3 kilogram/m.sup.2, of Gold Flex sheets was determined. The ballistic resistance was determined before liquid take up and expressed as energy absorption (Eabs) in the table below.

EXAMPLE 2

(6) The multilayer material sheet comprising aramid fibers as used in comparative experiment B was fed through a double belt press under the following conditions: a pressure of 8 MPa and a temperature of 150 C. for a time of 20 seconds, followed by cooling under pressure to 80 C. before exiting the double belt press. Again liquid uptake and ballistic resistance was determined in the same way as in comparative experiment B.

COMPARATIVE EXPERIMENT C

(7) Example 1 is repeated whereby the multilayer material sheet is fed through a double belt press at a pressure of 8 MPa and a temperature of 130 C. for a time of 10.5 seconds. In this experiment no cooling under pressure takes place.

(8) The results of the tests are shown in the table below.

(9) TABLE-US-00001 Sample Liquid uptake (wt %) Eabs [J*m.sup.2/kg] Comparative experiment A 9.0 Example 1 4.5 Comparative experiment B 135 243 Example 2 50 261 Comparative experiment C 8.0

(10) The above table clearly shows the reduced liquid uptake of the multilayer material sheets as obtained with the process according to the invention. Furthermore an increased ballistic resistance, expressed as a higher Eabs, was seen.