Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Patent
1998-03-27
2000-04-04
Martin, Roland
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
G03G 9097
Patent
active
060459603
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with improvements in and relating to powders, and in particular, powder toners for use as developers in electrostatographic reproductions apparatus. The invention is especially concerned with single component toners which may, for example, find use in apparatus wherein toner is maintained in a charged fluidised bed whence the charged toner is supplied to applicator means for applying it to the desired substrate. Such apparatus is described, for example, in EP-A-0 494 544.
Some conventional toners exhibit fluid properties (and in particular, liquid-like properties) when subjected to mechanical agitation and when return to rest, become compacted. However, the present invention is in part, derived from an unexpected observation that some toners which are new, exhibit much greater fluidity when subjected to mechanical agitation or aeration. This is a primary property of such toners. Normally, when the agitation is stopped, they eventually settle with a somewhat greater degree of compaction in comparison with the aforementioned known toners. This is in contrast to the conventional toners which do not achieve such a degree of compaction at rest. It has been found that this fluidization (and compaction) behaviour is an indicator marked suitability for use in apparatus of the kind described in EP-A-0 494 544. Many of these toners are also substantially free of properties which are disadvantageous when they are used in that apparatus.
However, in the broadest sense, this novel behaviour, and therefore the present invention, is not limited to toner compositions but in principle, to other compositions intended for other applications. Thus, in a first aspect the present invention provides a powder composition which exhibits fluid properties when subjected to mechanical agitation or aeration and which settles as a compacted solid when the aeration or agitation ceases, said composition exhibiting behaviour substantially free of slugging, channelling and jetting when aerated.
Preferred "fluidizable" powder compositions according to any aspect of the present invention include those which exhibit liquid-like behaviour when aerated in the aforementioned kind of fluidised bed described in EP-A-0 494 544, even if they do not exhibit a marked liquid-like behaviour upon mere mechanical agitation. These especially preferred compositions are not prone to slugging, channelling or jetting, and preferably also not to spouting when used in this apparatus. These terms are standard terminology for the behaviour of powders in fluidised bed systems and as used herein, have the meanings described in Ch. 6, D. Geldhart "Gas Fluidization" in M. J. Rhodes (Ed.) Principles of Powder Technology, Wiley 1990 (incorporated herein by reference), for example as explained in and with reference to FIG. 6.3 of the latter reference.
Compositions according to any aspect of the invention may be identified not only by their fluid-like behaviour when agitated, but preferably also by their degree of compaction in terms of the "compaction ratio" of such compositions. As used herein, the term compaction ratio means the ratio of the maximum height of the surface of the composition when vigorously agitated in a cylindrical container to the minimum height attained by the surface when at rest. Preferably, this compaction ratio is at least 3:2, more preferably at least 7:4.
In a second aspect, the present invention provides a fluidizable powder composition comprising particles of synthetic thermoplastic material blended with a (preferably surface-treated) particulate refractory metal oxide material.
Optionally, compositions according to either of the first or second aspects of the present invention may also possess the features of the other.
In the context of the present invention, the term "fluidizable" as applied to a powder composition includes those powder compositions which demonstrate the above-mentioned fluid behaviour upon aeration or agitation. Thus, the fluidity of the powder compositions in the aerated/agitated state is impor
REFERENCES:
patent: 5272040 (1993-12-01), Nakasawa et al.
Neilson Ian Stuart
Sturt Michael David
Coates Brothers PLC
Martin Roland
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