Abstract: An ink composition for ballpoint pens comprises a coloring agent, a liquid medium, a polyoxyethylene castor oil and/or a polyoxyethylene hardened castor oil, or a derivative thereof, and one compound or a mixture of two or more compounds selected from the group consisting of a monoalkyl ether phosphoric acid, a polyoxyethylene monoalkyl ether phosphoric acid, a dialkyl ether phosphoric acid, a polyoxyethylene dialkyl ether phosphoric acid, a trialkyl ether phosphoric acid, and a polyoxyethylene trialkyl ether phosphoric acid.

Abstract: A ballpoint pen ink ensuring a very soft and smooth writing feel even when a strong writing pressure is applied, is obtained. A ballpoint pen ink containing a colorant, a liquid medium, a polyoxyethylene castor oil and/or a polyoxyethylene hardened castor oil, or a derivative thereof, and one kind or a mixture of two or more kinds selected from a monoalkyl ether phosphoric acid, a polyoxyethylene monoalkyl ether phosphoric acid, a dialkyl ether phosphoric acid, a polyoxyethylene dialkyl ether phosphoric acid, a trialkyl ether phosphoric acid, a polyoxyethylene trialkyl ether phosphoric acid and their neutralization products or solutions.

Abstract: A washing liquid cartridge removably positionable in a writing instrument of the type having a removable ink container. The washing liquid container contains therein a washing liquid and has an engagement portion at one end removably engagable with an inner element of the writing instrument and an openable seal adjacent to the engagement portion. When the seal of the cartridge is opened and the cartridge is snugly fitted in position within the writing instrument in place of the ink container, the washing liquid in the cartridge flows and washes the ink passage within the writing instrument.