Plastics material mesh structures

Abstract

In order to provide wider biaxially-stretched geogrids having high primary direction (PD) strength, crotch-forming zones of a starting material which is at least 2.0 mm thick have protuberances ( ). On strectching, PD orientation passes right through the junction ( ) but the protuberance ( ) causes the orientation ratio of the crotch edge to decrease significiantly as orientation enters the central part of the crotch edge. After a secondary direction stretch of at least about 1.5:1, the thickness of the central part of the crotch edge is not reduced by more than about 20%. The stretching does not reduce the thickness of any point along notional ridge lines ( ) to such an extent that the ratio of finished thickness to starting thickness at that point mid-point. In the biax geogrid ( ), the junction mid-point is significantly thicker than the PD is less than about 80% of the ratio of finished thickness to starting thickness of the junction strand mid-point. The thickest part of the crotch is greater than about 80% of the thickness of the mid-point of the junction ( ). The junction ( ) has a generally square or rectangular central zone with narrow projections ( ) at the corners extending outwards to the crotch edges.