Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Patent
1994-08-15
1997-03-11
Duda, Kathleen
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
430111, 430113, 430137, G03G 908
Patent
active
056099797
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the production of microparticles particularly for electrostatographic processes.
BACKGROUND OF THE INVENTION
Prior art electrostatographic processes are known, such as photocopying and the like in which microscopic particles are attracted to latent images in the form of discrete electrostatic charges on the surface of a suitable recording member. Such microscopic particles, usually known as toner particles, may be applied to the surface to be toned in dry powder form, or as a suspension in an insulating liquid, usually a relatively high boiling point aliphatic hydrocarbon liquid or the like.
Many methods have been proposed for the production of such toners, both dry and liquid dispersed. Toner particles in the general sense normally contain at least a pigment or dye and a binder, such as a natural or synthetic resin or polymeric material. The so-called dry toners may also have admixed therewith flow improving agents such as colloidal silica or the like to enhance their functionality in the various toner applications in use, and in addition may be mixed with so-called carrier particles, usually magnetic, which act to transport the toner to the point of application. Such carrier particles are selected to bear the correct triboelectric relationship with the toner particles to allow correct toning functionality. Normal production methods are many and varied, the most common involving hot melt mixing followed by cooling, pulverising and grinding to obtain particles of the correct particle size, normally 1 to 10 microns mean diameter. Such processes are energy inefficient and in addition environmentally unattractive due to dust generation. A further problem exists that particles produced by such processes are not necessarily spheroidal and hence do not flow well in use.
Microencapsulation techniques have also been proposed to produce more or less spherical particles, but such processes are also energy inefficient as they normally involve spray drying of water slurries of quite low solids content.
Liquid dispersed toners can generally be produced using techniques which are more energy efficient and with no significant dusting problems. However, liquid dispersed toners of the prior art normally contain other materials in addition to the colouring matter and binder resin or polymer. Such materials include surfactants, stabilisers, charge modifiers and the like, and in many instances the binder resin or polymer is partly soluble in the dispersant or carrier liquid.
It is the object of the present invention to overcome these and other problems relating to the production of both dry and liquid dispersed electrostatographic toner particles.
SUMMARY OF THE INVENTION
In one form therefore the invention is said to reside in a method of production of microparticles of a material suitable as a toner for electrostatographic processes wherein the material is or includes a thermoplastic polymer, the method comprising the steps of melting the material in a continuous phase having a boiling point higher than the melting point of the material, the material being non-soluble in the continuous phase, mixing the material in the continuous phase to produce an emulsion and cooling the emulsion to produce a dispersion of solid microparticles of the material in the continuous phase.
Hence it can be seen that the present invention involves the mechanical emulsification of melted thermoplastic polymers into an incompatible non-solvent continuous phase. The action of surface tension forces in the emulsion of the material in liquid phase supported in the incompatible liquid continuous phase will allow spherical particles to be produced.
In a preferred form particularly where dry toners are to be produced the invention may include the further step of separating the microparticles so produced from the liquid.
Preferably there may be further included a surface active agent in the continuous phase which will assist in controlling or regulating the particle size of the microparticles. The surface active agent may
REFERENCES:
patent: 4794066 (1988-12-01), Taggi et al.
patent: 5017451 (1991-05-01), Larson
patent: 5270445 (1993-12-01), Hou
Patent Abstracts of Japan, vol. 12, No. 233 (p-724) (3080), Jul. 5, 1988 & JP-A-63 025 663 (Toyo Ink) Feb. 3, 1988-Abstract.
Patent Abstracts of Japan, vol. 11, No. 268 (c-444) (2715), Aug. 29, 1987 & JP-A-62 072 727 (Konishiroku) Apr. 3, 1987-Abstract.
Patent Abstracts of Japan, vol. 9, No. 186 (p-377) (1909), Aug. 2, 1985 & JP-A-60 057 350 (Showa Denko) Apr. 3, 1985-Abstract.
Patent Abstracts of Japan, vol. 16, No. 117 (p-1328), Mar. 24, 1992 & JP-A-03 287 174 (Dainippon Printing) Dec. 17, 1991-Abstract.
Duda Kathleen
Research Laboratories of Australia Pty Ltd.
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