Ballpoint writing instrument containing an initially erasable ink

Claim 1

In a ballpoint writing instrument containing a supply of ink capable of producing an intense colored line when deposited on a writing paper surface which line is capable of erasure within several hours after deposit by the use of a conventional pencil eraser without causing damage to the writing paper surface but which thereafter sets up to produce a permanent non-erasable line, said ink consisting essentially of an elastomeric polymer present in an amount between 20 and 36% by weight dissolved in an essentially non-volatile hydrocarbon solvent or plasticizer present in an amount between 36 and 68% by weight, said solvent or plasticizer being a light mineral oil having a viscosity at 20° C. of around 1.5 centipoises, being present in amount relative to said polymer such as to impart a final ink viscosity in the range 1-4X10 6 centipoises, and having a boiling point in the range 180°-290° C., and pigment particles present in the amount of 12 to 26% by weight evenly dispersed in the plasticized elastomer polymer solution, the pigment being present in amount relative to said polymer as to impart intensity while preserving the capability of initial erasure of said line.