Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Patent
1994-06-13
1996-03-05
Rodee, Christopher D.
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
430108, 430137, 428404, 427127, G03G 7113
Patent
active
054966744
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to novel particles (I) which are suitable as carriers for electrophotography and consist of silica, tin oxide or zirconium oxide or a mixture thereof.
The present invention also relates to further novel particles (II) which are suitable as carriers for electrophotography and consist of tetraalcoholate in the gas phase by reaction with steam and/or oxygen in the presence of agitated cores.
The present invention furthermore relates to processes for the preparation of these particles and their use for the preparation of electrophotographic two-component developers, and electrophotographic two-component developers which contain these particles.
Two-component developers are used in electrophotographic copiers and laser printers for developing an electrophotographically produced latent image and usually consist of carrier particles and toner particles. The carrier particles are magnetizable particles having sizes of, as a rule, from 20 to 1,000 .mu.m. The toner particles consist essentially of a color-imparting component and binder and have a size of about 5-30 .mu.m.
In the copying process, the electrostatic, latent image is produced by selective exposure of an electrostatically charged photoconductor roller to light reflected from the original. In the laser printer, this is effected by a laser beam.
For the development of the electrostatic image, toner particles are transported to the photoconductor roller by means of a magnetic brush, i.e. carrier particles oriented along the field lines of a sector magnet. The toner particles adhere through electrostatic attraction to the carrier particles and, during transport in the magnetic field, acquire an electrostatic charge opposite to that of the carrier particles, as a result of friction. The toner particles thus transferred from the magnetic brush to the photoconductor roller give a toner image which is then transferred to electrostatically charged paper and fixed.
The carrier particles used have to meet a number of requirements: they should be magnetizable and thus permit a rapid build-up of the magnetic brush. Furthermore, their surface should have low conductivity in order to prevent a short-circuit between the sector magnet and the photoconductor roller. This conductivity should remain constant over long operating times of the carrier so that the triboelectric charge of the developer can also be kept constant for a long time. Not least, the carrier particles should also be free-flowing and should not form lumps in the developer storage vessel.
In order to meet these requirements, the carrier particles consisting of magnetically hard or in particular magnetically soft material must as a rule be coated.
EP-A-303 918 discloses the coating of steel and ferrite carriers with iron oxide or titanium dioxide which is precipitated by oxidative or hydrolytic decomposition of iron pentacarbonyl or titanium tetrachloride from the gas phase onto the carrier particles.
It is also generally known that the surface of the carrier particles can be coated with polymers, in particular polymeric fluorocarbons, or the surface of metallic carrier particles can be passivated by oxidation.
However, the last-mentioned coating methods in particular have many disadvantages. Constant and sufficiently thick layers are difficult to produce and in addition polymer-coated carriers exhibit poor adhesion of the polymer layer to the carrier surface and therefore have only a short life.
It is an object of the present invention to provide novel carriers for electrophotography which possess advantageous performance characteristics, and hence to make it possible to achieve optimum matching of the carrier with the particular toner used.
We have found that this object is achieved by particles (I) which are suitable as carriers for electrophotography and consist of silica, tin oxide or zirconium oxide or a mixture thereof.
We have furthermore found a process for the preparation of the particles (I), wherein volatile aluminum, chlorine, molybdenum, tungsten, silicon, tin an
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Adel Joerg
Czech Erwin
Mronga Norbert
BASF - Aktiengesellschaft
Rodee Christopher D.
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