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Preparation of Water Based Magnetic Inks

IP.com Disclosure Number: IPCOM000089698D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 28K

Publishing Venue

IBM

Related People

Acitelli, MA: AUTHOR [+2]

Abstract

In the preparation of magnetic inks, oleate-coated magnetite is converted into a stable colloidal ink by use of a cationic and nonionic surfactant together with intimate mixing. The role of the cationic surfactant (usually an amino derivative) is to render the oleate-coated magnetite highly positive so as to enhance colloidal stability by electrostatic repulsion. The nonionic surfactant serves to decrease the surface tension of the magnetite particles, thus keeping it in suspension in an aqueous medium. In addition to cationic surfactants, anionic surfactants have been used successfully to prepare magnetic inks.

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Preparation of Water Based Magnetic Inks

In the preparation of magnetic inks, oleate-coated magnetite is converted into a stable colloidal ink by use of a cationic and nonionic surfactant together with intimate mixing. The role of the cationic surfactant (usually an amino derivative) is to render the oleate-coated magnetite highly positive so as to enhance colloidal stability by electrostatic repulsion. The nonionic surfactant serves to decrease the surface tension of the magnetite particles, thus keeping it in suspension in an aqueous medium. In addition to cationic surfactants, anionic surfactants have been used successfully to prepare magnetic inks.

An improved method of preparing stable, finely-dispersed magnetic inks involves the use of amphoteric surfactants, that is, compounds containing both carboxyl and amine functionality in their structure. The cationic center is either a secondary or tertiary amine group. The anionic properties are provided by the carboxylate group or groups. In acidic solution the surfactant is a cationic amine salt, and in alkaline solution it is an anionic carboxylate salt. If just the right amount of acid is present, the cationic and anionic properties balance and a "zwitterion" is obtained. This amphoterism can be represented as follows:

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Magnetic inks have been prepared using a series of such commercially available surfactants, including salts and free acid forms of both N-fatty amino- propionates and the N-fatty imino dipropionates. A variety of long chain R groups are available. These compounds may be represented as follows:

(Image Omitted)

The surfactant giving the best magnetic ink from a pproperty-and- performance viewpoint was DERIPHAT 151C* (N-Coco-B-amino propionic acid).

The advantage of using an amphoteric surfactant over either a cationic or anionic surfactant is that it is less sensitive to t...