The invention provides a direct-liquid type pen
ink sac, which solves the technical problems that in the prior art the leak tightness in the replacing process is poor, the increased amount of ink is hard difficult to control, spillover and splash
pollution are easy to generate, the manufacturing manufacture is difficult, and the like. The direct-liquid type pen
ink sac comprises a sac body, a neck matching hole, a valve matching hole formed on the inner side of the neck matching hole, and a valve, wherein the surface of the inner cavity of the sac body is formed provided with an elastic seat surface, the inner cavity of the sac body is provided with a spring of which the two ends
resist against the elastic seat surface and the valve, and the surfaces of the sac body and the valve matching hole are formed provided with capillary channels; and the neck matching hole consists of a step surface and a threaded segment. The direct-liquid type pen
ink sac has flexible and automatic leak tightness, can perform simple and convenient quantitative
perfusion with a matched ink
bottle without ink spillover, is convenient and reliable, has good hand feel in use, is sealed by a seal ring step surface and connected by threads, has lower requirement on the precision of plastic parts, and is suitable for
batch production; besides, the sac body can be used as a penholder and can be refilled with ink, thus the direct-liquid type pen ink sac has low writing cost is low and is particularly suitable for students and office work.