Writing medium for ball point writing instrument

Abstract

A writing medium capable of being erased by merely mechanically rubbing with an ordinary pencil eraser after writing and capable of forming a drawing line possessing high adhering strength onto the surface of paper even immediately after writing on the paper. The writing medium contains a pigment as a colorant, a polynorbornane and/or trans-1,4-polyisoprene, and a mixture solvent solution for dissolving the polynorbornane and the trans-1,4-polyisoprene and containing a low boiling point organic solvent having a boiling point of less than 180.degree. C. and a high vaporization rate and operating as a plasticizer for the polynorbornane and the trans-1,4-polyisoprene and a high boiling point organic solvent having a boiling point of higher than 300.degree. C. and a low vaporization rate. Thus, a drawing line written with the writing medium can be erased merely by rubbing with the eraser within several hours after writing, and is not erased thereafter.

Dependencies are inferred from the claim text.