Ball-point instruments writing with improved transitorially erasable trace and ink compositions therefor

Claim 1

In a ball-point writing instrument containing an ink capable of depositing an intensely colored trace by writing with its ball on paper, said trace being capable of erasure by the use of a pencil eraser, said ink consisting essentially of between 15% and 45%, by weight, of natural rubber or rubber which essentially duplicates the chemical structure of natural rubber, said rubber being dissolved in a mixture of (a) a volatile low boiling organic solvent having a boiling point less than 180° C and exhibiting 100% evaporation within 60 minutes, said volatile low boiling solvent rapidly increasing the viscosity of the ink in the trace to minimize the penetration of the paper by the ink, and (b) a high boiling organic liquid solvent having a boiling point of greater than 300° C, said vaporizable organic solvent being present in an amount of between 10% and 50%, by weight, and said high boiling organic liquid solvent being present in an amount of between 15% and 30%, by weight, and from 12% to 30%, by weight, of pigment particles uniformly dispersed in the rubber solution.