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Process for Purification of Magnetic Ink

IP.com Disclosure Number: IPCOM000083814D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Sambucetti, CJ: AUTHOR [+2]

Abstract

A known magnetic fluid is a colloidal suspension of oleic acid-coated Fe(3)O(4) (appr. 100 Angstroms dia.) dispersed in a mixture of TRITON* + ARQUAD** surfactants. In the process of converting the fluid into ink, controlled amounts of glycerol, polyethylene glycol and butyl CELLOSOLVE*** are added to achieve filterability, viscosity stabilization and desired paper-ink interaction.

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Process for Purification of Magnetic Ink

A known magnetic fluid is a colloidal suspension of oleic acid-coated Fe(3)O(4) (appr. 100 Angstroms dia.) dispersed in a mixture of TRITON* + ARQUAD** surfactants. In the process of converting the fluid into ink, controlled amounts of glycerol, polyethylene glycol and butyl CELLOSOLVE*** are added to achieve filterability, viscosity stabilization and desired paper-ink interaction.

In the dispersion process the following reaction is accomplished. (1) nSurfactant + Fe(3)O(4) -----> Fe(3)O(4) (surfactant) over (adsorbed) n, which
consists in adsorption (chemisorption) of surfactant molecules on the Fe(3)O(4) by intimately grinding the reagents in an attritor, followed by hot digestion of the mixture at about 90 degrees C. The surfactant molecules provide the Fe(3)O(4) particles with steric repulsion, electrostatic stabilizing charges, and besides, they make the particles compatible with the solvent (water) through their hydrophilic moietie.

It has been found, however, that in order to achieve efficient coating and dispersion of Fe(3)O(4), an excess of surfactant has to be used in the process. In fact, reaction (1) is driven by mass action law and an excess surfactant concentration is needed to drive the reaction to completion.

It can be estimated that a fluid of 25 emu/gr (35% Fe(3)O(4) by weight, density of Fe(3)O(4) = 2.75 g/cm/3/size = 100 Angstrom dia) contains of the order of 2 x 10/17/Fe(3)O(4) particles/cc. Density of ink approx. 1.36 g/cm/3/.

Assuming an average number of 10 surfactant molecules to stabilize a particle, a concentration of surfactant of: 2 x 10/17/ x 10 over 6 x 10/23/ . 1000 = 3 x 10/3/ mol/liter will be required to achieve total colloidal stabilization of Fe(3)O(4).

Now, the actual surfactant concentration used in the ink is: 40 grs (TRITON + ARQUAD) to obtain close to 500 grs of ink, (360 cc, divided by 2 because only half the fluid mass is water), which gives a total surfactant concentration of 0.3 molar (assuming 600 as the average molecular weight of TRITON + ARQUAD).

Some of the excess surfactant is eliminated in the centrifugation step. But even assuming that this is equal to 1/2 the total surfactant concentration added
(0.3 M/2) and that the number of surfactant molecules associated with Fe(3)O(4) is ten times larger (100 molecules per Fe(3)O(4) particle), still the free surfactant in excess is 0.12 molar.

As the critical micelle concentration for TRITON or ARQUAD is at least 1x10/-4/ molar, the ink medium is definitely prone to large micellar formation. The micelle aggregates can grow into large sizes, inc...