Charge Director for Liquid Toner

Abstract

A charge director material for charging a liquid toner, the charge director material comprising (a) nanoparticles of a simple salt and (b) a sulfosuccinate salt of the general formula MAn, wherein M is a metal, n is the valence of M, and A is an ion of the general formula (I)[R1—O—C(O)CH2CH(SO3−)C(O)—O—R2],  (I)wherein each of R1 and R2 is an alkyl group;said charge director material being substantially free of acids of the general formula (I),wherein one or both of R1 and R2 is hydrogen, and if only one of them is hydrogen, the other is an alkyl group,

Description

RELATED APPLICATIONS[0001]This application claims priority to, and is a US National Phase of, International Patent Application No. PCT / US2006 / 018297, having title “CHARGE DIRECTOR FOR LIQUID TONER”, having been filed on 10 May 2006 and having PCT Publication No. WO2007 / 130069, commonly assigned herewith, and hereby incorporated by reference.FIELD OF THE INVENTION[0002]The present application discloses charge directors in liquid electrography, some chemical materials useful as such charge directors, and methods for obtaining and using said materials.BACKGROUND OF THE INVENTION[0003]In many printing systems, it is common practice to develop a hardcopy of an image by using a photoconductive surface. The photoconductive surface is selectively charged with a latent electrostatic image having image and background areas. A liquid developer comprising charged toner particles in a carrier liquid is brought into contact with the selectively charged photoconductive surface. The charged toner p...

AI Technical Summary

Benefits of technology

[0012]A system of electrically stabilized charge director containing one charge director component, may be free of the above described drawbacks and therefore, the charge director concentration in the carrier liquid may be easily controlled. Another possible advantage is chemical stability during short or long term printing operation in the press.

[0015]Optionally, the micelle forming salt is a salt of a dialkyl ester of succinic acid. In some embodiments of the invention, the charge director material is free of acidic hydrolysis products of the diester. While the alcoholic products of hydrolysis may be tolerated, and in some cases even beneficial, being free of acidic hydrolysis products appears to be highly advantageous in these embodiments, whether the acidic hydrolysis products appear in the charge director material as result of hydrolysis, or because of any other reason. Absence of acidic hydrolysis products increases the charging of the charge director, lengthens its shelf life, and may decrease the charge director sensitivity to humidity and to some pigments.

[0019]In some embodiments it is also advantageous to have the charge director material free of the acid HA, where A is as defined above. This may lengthen the shelf life of the charge director material, increase its charging capability, and improve print quality.

[0023]To improve reproducibility of the method, it may be advisable to workup the sulfoccinic acid before it is reacted with a base, such that anions of the strong acid are removed before the base is added. It was surprisingly found that compounds obtained this way were poor charge directors. To improve charging, it is possible to add or otherwise provide nanoparticles of a simple salt to the poor charge director. Additionally or alternatively, the reaction with the base may be carried out in the presence of another ionic substance (other than a metal salt of dialkyl sulfosuccinate) that may react with the base to provide the nanoparticles.

[0026]Another aspect of some embodiments of the present invention is a liquid developer comprising charge director material in accordance with the present invention. In exemplary embodiments, the liquid developer may be of the kind disclosed in U.S. Pat. No. 5,346,796, the disclosure of which is incorporated herein by reference, with a charge director of the present invention replacing the charge director mentioned in the reference. The developer with the presently disclosed charge director was found to have many advantages on the developer that was prepared exactly according to the prior art. It gave less background printing, images with sharper edges, and proved much less water-sensitive. Furthermore, a liquid developer of the invention was able to retain a constant ink particle charge, while printing low coverage impressions in a much greater number than obtained with a prior art charge director.

Problems solved by technology

A possible disadvantage of using a mixture of materials as charge director is the possibility of selective adsorption of certain charge director components onto the surface of the ink particles.

This may lead to differential depletion of the components responsive to their affinity to the ink particles.

Therefore, a non-controllable change in the charge director composition may be expected during continuous printing process.

This may adversely affect the long term characteristics of the charge director and reflected in degraded print quality.

Such prior art charge directors may suffer from gradual irreversible adherence of the soybean extract onto the photoconductor surface, which may be reflected in lateral conductivity on the photoconductor, resulting in degraded print quality.

Many non-synthetic charge director components are highly sensitive to water, and therefore, the ink or toner comprising them may change its conductivity upon changes in humidity.

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