MATERIAL SHEET AND PROCESS FOR ITS PREPARATION
The invention relates to a material sheet comprising a woven fabric of polymer tapes, wherein the width of a tape varies less than 2% on average in the longitudinal direction of the tape. The invention also relates to a process for the preparation of the material sheet, and to a ballistic resistant article comprising the material sheet. A ballistic resistant article comprising the material sheet exhibits excellent antiballistic properties.
1 . A process for the preparation of a polymeric tape having a width that varies less than 2% on average in the longitudinal direction of the tape, the process comprising forming a polymeric powder bed, compression-moulding the polymeric powder bed at a temperature below the melting point of the polymeric powder, and wherein the powder bed is moulded by compression together with at least one compressible border element positioned onto the powder bed to partition said powder bed into at least two parts, said compressible bordering element being made of a compressible material.
2 . A process according to claim 1 , comprising drawing the compression-moulded polymer.
3 . A process according to claim 2 , wherein drawing is carried out in multiple steps.
4 . A process according to claim 3 , comprising multiple drawing at increasing temperatures.
5 . A process according to claim 1 , wherein the polymer from which the polymeric tape is made is selected from the group consisting of polyolefins, polyesters, polyvinyl alcohols, polyacrylonitriles, and polyamides.
6 . A process according to claim 1 , wherein the polymeric tape comprises ultra high molecular weight polyethylene.
7 . A process according to claim 6 , wherein the ultra high molecular weight polyethylene polymer used in this process is drawable in the solid state.
8 . A process according to claim 1 , wherein the at least one compressible border element includes at least one compressible strip made of a material having a melting temperature as determined by DSC of at least 10° C. higher than the melting temperature of the polymeric powder.
9 . A process according to claim 8 , wherein the compressible strip is formed of a thermoplastic polymer.
10 . A process according to claim 8 , wherein the compressible strip is formed from polypropylene, rubber polymer or silicon rubber.
11 . A process according to claim 8 , wherein the compressible strip has a rectangular, triangular, circular, or polygonal cross-section.
12 . A process according to claim 8 , wherein the compressible strip comprises a hose or a tube.
13 . A process according to claim 12 , wherein the compressible strip has a ratio of outer diameter: inner diameter of 3:2, 3:1.5 or 3:1.
14 . A process according to claim 8 , wherein the compressible strip has an undeformed height which is equal or higher than an undeformed average thickness of the polymeric powder bed.