Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-11-22
2002-07-16
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
Reexamination Certificate
active
06420029
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to coated particles. It relates especially to coated carrier particles to be used as carrier particles in multi-component developers for electrostatic imaging with magnetic brush development as well in cascade development.
BACKGROUND OF THE INVENTION
In electrostatographic imaging, carrier particles, mostly magnetic carrier particles, are mixed with toner particles (and with other ingredients) to form a developer. When the developer is to be used in magnetic brush development, the carrier particles are magnetic, and when the developer is used in cascade development, the carrier particles can be coated glass beads. In any case, the rubbing of the carrier particles and the toner particles induce a tribo-electric charge in the toner particles and the nature of the coating on the carrier particles determines, together with the toner ingredients, not only the polarity of the charge on the toner articles and the amount of the charge but also the stability of the charge over time, the charge distribution over the population of toner particles, etc. Thus the coating of the carrier particles is very crucial to the resulting properties of the developer and thus to the image quality that can be reached with that developer. Also the speed of charging of the toner particles is to a large extent determined by the coating of the carrier particles. Carrier particles having a high speed of charging towards the toner particles are beneficial, especially when images with high image fill (i.e. a high amount of area in an page is really occupied by toning particles) are present. Then, large amounts of toner are consumed and the toner, especially in long run printing, resides only a limited time in the developer. In such a situation, the toner has only a limited number of activation cycles. Hence, the charging properties of the developer, in terms of its kinetics, i.e. the speed of the rise of the charge amount, as well as in terms of its plateau value, are important.
In JP-A-10 153 886 it is disclosed to apply on carrier particles for use in electrostatographic developers a coating of a polyester with relatively high acid value and tri-alkyloxysilane compounds that contain groups that can react with the free acid groups of the polyester.
In WO-A 98/53372 a new type of coating has been described, consisting of chemical compounds selected from the group consisting of a monomeric polyfunctional organosilane, a hydrolysis product of a monomeric polyfunctional organosilane, a reaction product of a monomeric polyfunctional organosilane with an organosilane containing a hetero-atom and a reaction product of a monomeric, polyfunctional organosilane with an alkoxide. Such a coating offers interesting properties, as described in said application. Moreover in EP-A 898 206 it has been disclosed that such a coating could be applied to carrier particles in a simple method that requires only mechanical stirring and uses a low amount of solvent.
The coating disclosed in WO-A 98/53372 produced with the method described in EP-A 898 206 has a very long lifetime and can easily be manufactured in an inexpensive method. However, it is shown that the coating shows some limitations in terms of activation behaviour, i.e. the charging of the toner particles in rubbing contact with the carrier coating shows relatively low speed and thus when images with high page fill have to be printed, some problems with charging can occur.
There is thus a further need for improvement in the activation property for such coatings. Moreover it has been found that this tendency is quite general. Silicon-atom containing coatings seem to have a lower activation property, and so it is described in the literature to add charging agents to such coatings. At the same time it is observed that the incorporation of these charging agents gives some instabilities to the manufacturing method described previously. In particular, coagulation and/or agglomeration occurs to some extent, thus giving rise to composition differences in the coating and hence differences in properties of the coated particles.
There is thus still a need to improve the performance of coated particles in general and carrier particles.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a coating composition whereby the coating can be designed in a flexible way to incorporate new properties and performances in this coating especially with respect to the speed of charging.
It is a further object of the invention to provide a coating composition whereby said coating can be applied in an easy, inexpensive and controllable way, resulting in a thin homogeneous layer without interruptions on the surface of the particles.
It is a further object of the invention to provide a coating composition whereby said coating can be applied in such a way that the composition of said coating on different particles of said coated particles population is similar to a high extent, inducing similar properties all over the coated particles and that during coating no or very few agglomerates are formed.
Further objects and advantages of the invention will become clear from the detailed description hereinafter.
The objects of the invention are realised by providing carrier particles having a coating comprising a polycondensation network having moieties derived from chemical compounds selected from the group consisting of a monomeric polyfunctional organosilane, an organosilane containing a hetero-atom and an alkoxide, characterised in that said coating further comprises an amount A of a polymeric compound not containing silicon atoms so that 5%≦A≦50% by weight, with respect to the weight of the dried coating.
DETAILED DESCRIPTION OF THE INVENTION
The quality of a coating for carrier particles according to the chemistry disclosed in WO-A 98/53372, that is included herein by reference, could surprisingly be enhanced with respect to the activation, i.e. the speed of charge accumulation on toner particles by rubbing contact between the carrier and the toner particles, when appreciable amounts of a non silicon containing polymeric substance were included in the coating. It was found that between 5 and 50 by weight, both limits included, of such non silicon containing polymeric compounds could be incorporated in the coating. Preferably an amount between 10 and 30% by weight, both limits included, is incorporated. Very surprisingly it was shown possible to incorporate such amounts of non silicon containing polymeric compounds in the coating using the method that was disclosed in EP-A 898 206 without problems of agglomeration and in a very reproducible way, although when said method was used for coating the particles with the same non silicon containing compound alone severe agglomeration occurred. It seems, without being bound to any theory, that the non silicon containing polymeric compound is essentially trapped in the polycondensation network forming a complex or an interpenetrating network.
Thus carrier particles according to this invention comprise a coating comprising a polycondensation network having moieties derived from chemical compounds selected from the group consisting of a monomeric polyfunctional organosilane, an organosilane containing an hetero-atom and an alkoxide, characterised in that said coating further comprises an amount A of a polymeric compound not containing silicon atoms so that 5%≦A≦50% by weight, with respect to the weight of the dried coating.
In a preferred embodiment, said polycondensation network is derived from 20 to 80% by weight of polyfunctional organosilane, 20 to 80% by weight of alkoxide, and 0 to 10% by weight of organosilane (I) which contains a hetero atom. In a more preferred embodiment, said polycondensation network contains 19.9 to 80% by weight of polyfunctional organosilane, 19.9 to 80% by weight of alkoxide (II), and 0.1 to 10% by weight of organosilane (I) which contains a hetero atom.
The polycondensation network can in addition to the chemicals above contain finely divided meta
Heitzmann Daniel
Tavernier Serge
Knobbe Martens Olson and Bear LLP
Le Hoa T.
Xeikon International
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