Ink for writing instrument has a ball tip, such as a ball point pen is

摘要

Writing medium for a ball point writing instrument comprises (a) a pigment, (b) a polynorbornane having repeating units of formula (I), and (c) a mixed solvent for the (I) comprising (i) a low b.pt. organic solvent with a b.pt. of less than 180 deg.C and a high vapourisation rate which serves as plasticiser for the (I), and (ii) a high b.pt. organic solvent with a b.pt. of over 300 deg.C and a low vapourisation rate. Pref. compsn. contains (by wt.) 12-30% (a), 15-45% (b), 10-50wt.% (c i) and 15-35% (c ii). The compsn. may also contain a trans-1,4-polyisoprene, the solvent mixt. (c) being capable of dissolving and plasticising the trans-1,4-polyisoprene. Pref. low b.pt. solvents (c i) are xylene, heptane or hexane and the high boiling solvents.