Patent ID: 7575385

Claim:
A double-head writing instrument, comprising: a barrel formed by injection molding of transparent synthetic resin, the barrel opened at first and second ends thereof, the barrel having a partition formed therein; first and second ink-tanks provided inside the barrel and defined by the barrel and the partition so as not to communicate each other, the first and second ink-tanks opened at the first and second ends of the barrel, respectively; a first ink-retaining member connected with a first nib provided on an opening of the first ink-tank; a first ink reserved inside a first ink-reservoir which is provided inside the first ink-tank and at rear of the first ink-retaining member; a second ink-retaining member connected with a second nib provided on an opening of the second ink-tank; and a second ink reserved inside a second ink-reservoir which is provided inside the second ink-tank and at rear of the second ink-retaining member, wherein the first and second ink-retaining members retain temporarily the first and second ink spilled in accordance with an increase in pressure inside the first and second ink-reservoirs, respectively, and the partition is extended in an axial direction of the writing instrument so as that the first and second ink-reservoirs overlap each other in a radial direction, wherein a distance defined between an end of the first nib side of the partition connected to the barrel and the rear end of the first ink-retaining member is different from a distance defined between an end of the second nib side of the partition connected to the barrel and the rear end of the second ink-retaining member; wherein a capacity A of the first ink reservoir is larger than a capacity B of the second ink reservoir, and a ratio between the capacities B/A is between 0.3 and 0.8; and wherein the first nib and the second nib are formed by fiber modifications, porous material or brush bodies.