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Magnetographic Copier and/or Line Printer Utilizing Capillary Magnetic Ink Dispensing Technique

IP.com Disclosure Number: IPCOM000081847D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 4 page(s) / 57K

Publishing Venue

IBM

Related People

Romankiw, LT: AUTHOR

Abstract

This technique dispenses and transfers magnetic ink directly onto untreated paper wherein the ink contacts the paper only when a character is to be formed, and neither heating nor baking on of the ink is needed.

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Magnetographic Copier and/or Line Printer Utilizing Capillary Magnetic Ink Dispensing Technique

This technique dispenses and transfers magnetic ink directly onto untreated paper wherein the ink contacts the paper only when a character is to be formed, and neither heating nor baking on of the ink is needed.

It has been demonstrated that when capillaries are formed perpendicular to a 5-to-50-mil thick hydrophobic sheet (such as polyethylene, polypropylene or TEFLON* and a water base magnetic ink such as ferrofluid is placed on one side of the hydrophobic surface, the ink does not flow through the capillaries to the opposite side of the sheet unless a magnet is brought near the opposite side of the sheet. Illustratively, plain bond paper was placed between a polypropylene film surface and the magnet. The ink was drawn through the polypropylene and an image was formed on the paper. The size of the ink spot which is formed depends on:
(1) The length of time the magnet is near the capillary (t).
(2) The magnetic moment of the ink (M(s)).
(3) The wetting characteristics of the dispensing surface

and of the paper by the ink, which involve:

(a) The radius of the capillary (r).

(b) The surface tension of the ink (gamma).

(c) The contact angle which the ink forms with the

dispenser hydrophobic surface (theta).

(d) The length of the capillary (l).

(e) The contact angle which the ink forms with

the paper.

(f) The magnitude of the capillary forces in the paper

for drawing (imbibing) the ink.
(4) If a cylindrical geometry is used for a dispenser, such

as shown in Figs. 2 and 3, the size of the drop, in

addition, depends on the centrifugal force with which

the fluid is forced through the capillaries due to

rotation of the drum.
(5) Pressure or vacuum applied to the ink reservoir

pneumatically or using piezoelectric or other similar

transducer. This vacuum or pressure can be constant

or intermittent, as desired.

The phenomenon involved is illustrated in Fig. 1. For a nonwetting surface immersed in an aqueous solution, the pressure drop deltaP can be expressed by the equation delta P = 2 gamma over r (cos theta). For a totally non-wetting system, theta = 180 degrees, and the equation reduces to delta P = 2 gamma over r which is equal t the hydrostatic pressure delta rho gh where: rho is the specific gravity of the fluid, g is the gravity constant, and h is the height of the head in the capillary. In order for the ink to be drawn through the capillary, the force exerted by the magnetic field has to exceed not only the opposing capillary forces DeltaP = 2gamma over r(cos theta), but it also has to exceed the pressure drop created due to the flow of the ink through the capillary of length l. The rate at which the ink is supplied is proportional to the magnitude of the magnetic field

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gradient in excess of the opposing capillary forces and the pressure drop created due to flow of the liquid.

Once the ink wets the paper, the capillary force...