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

Abstract

The invention relates to a process for the manufacture of a multilayer material sheet comprising unidirectional high performance fibers, the process comprising 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 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 invention furthermore relates to the multilayer material sheet obtainable with the process according to the invention. This multilayer material sheet has a reduced uptake of liquids.

Claims

1. A process for the manufacture of a multilayer material sheet comprising unidirectional high performance fibers with a tensile strength of at least 1.0 GPa and a tensile modulus of at least 40 GPa, the process comprising the steps of: (a) positioning the fibers in a parallel fashion, (b) consolidating the parallel fibers to obtain a monolayer by embedding at least a part of the fibers in a matrix material which is present in an amount of less than 20 wt. % based on the total weight of the monolayer, (c) stacking at least two monolayers such that a fiber direction in one monolayer is at an angle 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) using a belt press which subjects 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 process according to claim 1, wherein step (d) is practiced at a temperature of 85 to 135 C.

3. The process of claim 1, wherein the high performance fibers are high performance polyolefin fibers.

4. The process of claim 3, wherein the high performance polyolefin fibers are obtained by a gel spinning process.

5. The process of claim 3, wherein the high performance polyolefin fibers are high performance polyethylene fibers.

6. The process of claim 1, wherein the high performance fibers are aramid fibers.

7. The process according to claim 1, wherein step (e) includes subjecting the pressure and temperature treated stack of at least two fixed monolayers formed by step (d) to controllable rapid cooling under pressure using the belt press.

8. The process according to claim 1, wherein the pressure treatment during fixation according to step (d) is done under isobaric conditions.

9. The process according to claim 1, wherein step (b) is practiced by embedding at least part of the fibers in less than 15 wt %, based on the total weight of the monolayer, of the matrix material.

Description

EXAMPLE 1

(1) 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.

(2) Comparative Experiment B

(3) 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

(4) 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.

(5) Comparative Experiment C

(6) 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.

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

(8) 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

(9) 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.