Retroreflective microprismatic material and method of making same

A microprism retroreflector material having a body portion with a planar front face and closely spaced microprisms extending thereacross in a plane spaced from and parallel to said front face, said microprisms having a spacing between their apices of 0.006-0.025 inch, each of said microprisms being formed with three side surfaces disposed along three intersecting planes:

• (a) at least some of said microprisms having at least one side surface which is arcuate along one of said intersecting planes and over at least the major portion of its height, the ratio of the length of the radius defining the arc to the length of the base of said one side surface being 40-90:1 and effecting a divergence of reflected light of 17-25 milliradians;
• (b) at least some adjacent pairs of microprisms having their prism axes tilted 3-10.degree. relative to the intersecting plane extending therebetween;
• and
• (c) the intersection of the three surfaces defining included angles of 89.8-90.2.degree., whereby said microprisms, retroreflect light in six circumferentially spaced radially extending exit-energy patterns disposed about a central zero order cone, at least 70 per cent of the retroreflected light being within a spread of not more than 0.6.degree. from the light rays impinging thereon.