1. Field of the Invention
The present invention relates to writing instruments, and more particularly to a replaceable ink cartridge having a vent plug disposed in the rear end thereof.
2. Description of the Related Art
Writing instruments utilizing replaceable ink cartridges, and in particular those having ball point tips, are well known in the art to which the subject invention appertains. In the past, it has been observed that ink contained within a cartridge may seep out of the ball seat and leak from the cartridge tip to impede or prevent use of the writing instrument. Those skilled in the art have determined that this problem may result from the accumulation of excessive humidity within the cartridge body. Several mechanisms have been devised to limit the accumulation of humidity within the ink cartridge of a ball point writing instrument including those described, for example, in U.S. Pat. Nos. 2,877,744 to Ray, 3,282,254 to Malta et al., 3,698,825 to Sears et al., and 4,565,463 to Otaguro et al. Each of these patents describe vent plugs adapted to limit air flow to and from the interior of an ink cartridge. In the '744 patent to Ray, for example, an end plug is provided for a ball point pen which is formed with an elongated passage to permit the atmosphere to find access to the inside of the pen. In the '254 patent to Maim et al., a plug is described which is formed with a circular pathway for communicating the interior of the cartridge with ambient atmosphere.
Writing instruments having a retractor mechanism for moving an ink cartridge between a retracted position wherein the applicator tip is disposed within the pen body and a protracted position wherein the applicator tip is disposed outside the pen body are also well known in the art to which the subject invention appertains. Examples of retractable writing instruments are described in U.S. Pat. No. 3,326,189 to Baer and U.S. Pat. No. 4,221,490 to Maim. These instruments provide a plunger component disposed at the rear end of the pen for actuating the retractor mechanism to move the cartridge. In this type of writing instrument, it has been observed that a problem in the performance of the instrument may occur in that ink may separate from the ball point tip of the cartridge when the plunger is impacted by an undesirably large force, i.e. if dropped to the floor from a desktop. Generally, the end of the cartridge abuts the plunger component, which is rigidly secured in the body of the instrument. The impact caused by dropping the instrument causes the ink to move within the cartridge, since the cartridge itself is immovable with respect to the plunger and body of the instrument. Once the ball point tip and the ink in the cartridge have separated, the cartridge is rendered inoperative and must be discarded.
Yet another problem has been recognized in connection with ball point pens which involves dislocation of the ball point tip. This problem can result from the exertion of an undesirably large force on the applicator tip while writing, which will cause the ball point tip to be pushed from its seat and become lodged within the ink cartridge. In addition, dropping the pen on its tip may damage the tip, wherein the ball becomes unseated and disconnects from the pen. Dislocation of the ball from its seat, of course, will render the cartridge inoperative.
The present invention is directed to a cartridge, and in particular a vented plug disposed in the rear end of an ink cartridge, which overcomes the problems that have been observed in the art of ball point writing instruments.