Writing instrument with ball point and two reservoirs
AssigneeThe Gillette Company
InventorsCharles P. Kiricoples, Henry Behrens, Robert L. Brown
Life of this patent
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Abstract
A ball-point writing instrument in which dislodging of the rotating ball as a result of accidental droppage on a hard surface is prevented by employing an ink reservoir construction designed to prevent propagation of a travelling pressure step in the column of ink above the rotating ball.
Claims14
A writing instrument comprising a tubular barrel in association with a writing tip having a rotatably mounted ball, said writing instrument having ink-filled first and second ink reservoirs in fluid communication with each other, the ink in said second ink reservoir also being in fluid communication with said ball and forming a liquid-gas interface with a body of gas contained in said second ink reservoir, the longitudinal distance between the liquid-gas interface and the rotatably mounted ball not exceeding the critical liquid column height for the writing instrument where the critical liquid column height (CLCH) has the following definition:
- ##EQU2## g=acceleration of gravity (i.e. 386 inches/seconds.sup.2) e=ink density (pounds/inch.sup.3)
- t=pen barrel wall thickness (inches)
- 2R=wall diameter (inches)
- h=drop height (inches)
- (.sqroot.2gh)=impact velocity (inches/sec.)
- E.sub.I =bulk modulus of ink (pounds/inch.sup.2)
- ShL=socket holding length (i.e. the allowable axial movement of the ball within the ball socket without dislodgment, in inches)
- r=radius of the ball (inches)
- ball weight=weight of rotatable ball (pounds)
- E wall=modulus of elasticity of pen barrel wall (pounds/inch.sup.2) and
- F.sub.ret. min. =minimum point retention force (pounds).
A writing instrument comprising a tubular barrel in association with a writing tip having a rotatably mounted ball, said tubular barrel having an upper barrel portion and a lower barrel portion which are in fluid communication and which are separated by a member providing the effect of a liquid-gas interface, the longitudinal distance between the surface of said member providing the effect of a liquid-gas interface and the rotatably mounted ball not exceeding the critical liquid column height for the writing instrument where the critical liquid column height (CLCH) has the following definition:
- ##EQU3## g=acceleration of gravity (i.e. 386 inches/seconds.sup.2) e=ink density (pounds/inch.sup.3)
- t=pen barrel wall thickness (inches)
- 2R=wall diameter (inches)
- h=drop height (inches)
- (.sqroot.2gh)=impact velocity (inches/sec.)
- E.sub.I =bulk modulus of ink (pounds/inch.sup.2)
- ShL=socket holding length (i.e. the allowable axial movement of the ball within the ball socket without dislodgment, in inches)
- r=radius of the ball (inches)
- ball weight=weight of rotatable ball (pounds)
- E wall=modulus of elasticity of pen barrel wall (pounds/inch.sup.2) and
- F.sub.ret. min. =minimum point retention force (pounds).
A writing instrument comprising a tubular barrel in association with a writing tip having a rotatably mounted ball, said tubular barrel having an upper barrel portion and a lower barrel portion which are in fluid communication and which are separated by a member of closed cell foam, the longitudinal distance between a surface of said foam member and the rotatably mounted ball not exceeding the critical liquid column height for the writing instrument where the critical liquid column height (CLCH) has the following definition:
- ##EQU4## g=acceleration of gravity (i.e. 386 inches/seconds.sup.2) e=ink density (pounds/inch.sup.3)
- t=pen barrel wall thickness (inches)
- 2R=wall diameter (inches)
- h=drop height (inches)
- (.sqroot.2gh)=impact velocity (inches/sec.)
- E.sub.I =bulk modulus of ink (pounds/inch.sup.2)
- ShL=socket holding length (i.e. the allowable axial movement of the ball within the ball socket without dislodgment, in inches)
- r=radius of the ball (inches)
- ball weight=weight of rotatable ball (pounds)
- E wall=modulus of elasticity of pen barrel wall (pounds/inch.sup.2) and
- F.sub.ret. min. =minimum point retention force (pounds).
Dependencies are inferred from the claim text.