Patent ID: 7726894
Filing Date: 2010-06-01
Classification: B43K

Abstract:
1. A screw-type writing instrument having an expansion and contraction function with a retractable pen core, comprising: an outer shaft cam, with a first screw groove formed in a circumferential inner surface of the outer shaft cam; a cartridge holder having at a first side thereof a first screw, screwed into the first screw groove, and having at a second side thereof a second screw; an inner shaft cam, with a second screw groove formed in a circumferential inner surface of the inner shaft cam, so that, when the cartridge holder is coaxially inserted into the inner shaft cam, the second screw is screwed into the second screw groove; and an outer casing, comprising: a head part having a seating hole therein, so that a mounting part of the inner shaft cam is coaxially inserted into the seating hole; and a plurality of blades each extending a predetermined length from an end of the head part, wherein the outer shaft cam and the outer casing are coupled to each other, such that, when an axial length of the writing instrument is expanded or contracted by linear movement of the outer shaft cam and the outer casing with respect to each other, a tip of the pen core coupled to the cartridge holder is advanced from or retracted into a tip hole of the outer shaft cam, and wherein, for engagement of the outer shaft cam with the blades, first two opposite surfaces of the outer shaft cam protrude relatively outwards, while second two opposite surfaces thereof are bulged in a shape having a circumferential outer surface corresponding to a circular inner diameter, so that the blades of the outer casing slidably engage with the second two opposite surfaces.