Ballpoint writing instrument containing an initially erasable ink

摘要

A ballpoint writing instrument containing a supply of ink capable of producing an intense colored line when deposited on a writing paper surface that 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. The ink includes an elastomeric polymer such as Cis-1.4 Polyisoprene dissolved in an essentially non-volatile hydrocarbon solvent or plasticizer such as a light mineral oil and a colorant such as pigment particles evenly dispersed in the plasticized elastomeric polymer solution. The elastomeric polymer prevents the pigment colorant from penetrating into the writing paper surface. The preferred ink formulations also avoid or limit the use of volatile solvents which are detrimental to smooth writing characteristics for a ballpoint pen.