Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-12-09
2002-07-02
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S447000, C428S702000, C430S106100
Reexamination Certificate
active
06413638
ABSTRACT:
This invention relates to coated particles, particularly particles with an inorganic content, preferably purely inorganic particles and most preferably coated magnetic particles, which are used as carrier particles in electrostatographic developers for the electrostatographic production of images.
There is a series of electrostatographic printing methods which are known, e.g. direct electrostatic printing, in which toner is deposited by means of an electronically addressable print head on to a receiver material which does not comprise a latent electrostatic image.
In another form of electrostatic printing, toner formers are produced on an image-producing element in the form of a rotating drum which contains an electrostatic layer which consists of a multiplicity of controllable electrodes in and under a dielectric layer. An electrical voltage is generated in the controllable electrodes, according to the image, and attracts toner particles from a toner source.
In addition, it is known that in electrographic printing and in electrophotographic copying a latent electrostatic image can be produced, either of an original to be copied or for digitised data which describe an image which is accessible electronically.
In electrophotography, a latent electrostatic image is produced by the steps of a) charging a photoconductive element congruently, and b) discharging according to the image by an exposure which is modulated image by image.
In electrographics, a latent electrostatic image is produced by the deposition of electrically charged particles corresponding to the image, e.g. on a dielectric substrate by an electron beam or by ionised gas.
The latent image formers obtained are developed, namely they are converted to visible images by depositing substances on them which selectively absorb light; these substances are called toners and usually carry a triboelectric charge.
Two techniques are used for the toner development of latent electrostatic images: dry powder and liquid dispersion development, with dry powder development being the more commonly used.
Dry powder development can be carried out in various ways. One method is the single component method, in which the toner itself is charged by friction, transported by a roller and deposited on the latent image. The quality is limited, particularly if coloured prints are to be produced. Another method utilises liquid development, in which colloidally charged toner particles are applied to the photoconductor in a liquid insulating medium, e.g. a hydrocarbon. One disadvantage of this method is the emission of volatilised organic substances, particularly when high printing speeds are employed. A third method utilises a two-component developer. In this case, large-grained carrier particles which can be attracted magnetically form a magnetic brush on the surface of the developer roll, by forming the magnetic hairs of the brush. Triboelectrically charged toner particles are present on the surface of the carrier particles. These are stripped from the carrier particles according to the electrical charge of the latent electrostatic image, whereby the toner image is produced. In this method, the carrier particles are reused repeatedly; their mechanical stability is therefore particularly important.
Non-magnetic electrophotographic developers comprising two components can also be used as an alternative to what is termed the magnetic brush. In one particular embodiment, the developer consists of small glass spheres, which arc optionally coated, and of toner particles.
The developer is caused to deposit on the element carrying the latent image and in this manner causes development, as is described in BE 828 210. The carrier particles are also reused in this case.
In the case of surface-coated carrier particles, the stability of the surface coating is particularly important. Insufficient mechanical stability results in losses of quality of the printed image, and the developer has to be replaced, which causes unnecessary stoppages and cost.
A material with anti-adhesion properties is preferred for coating the carrier particles, in order to prevent the toner from sticking to the carrier surface. In most cases, however, this leads to a decrease in the adhesion of the coating on the carrier, which results in a shortening of the service life, e.g. when silicone resins are used as carrier coating media.
Carriers are known from U.S. Pat. No. 4,977,054 which consist of a magnetic powder and a silicone resin coating. The silicone resin used consists of D and T structural units (in D units the silicon atom is linked to further silicon atoms via 2 oxygen atoms, in T units it is linked via 3 oxygen atoms), wherein other functional organosilanes, such as di- and trialkoxy-functional organosilanes and/or di- and trialkoxy-functional organosilanes which contain nitrogen, can also be added in addition. Deposition is effected, as can be inferred from the examples, in a fluidised bed reactor; thereafter, the coatings are also cured at 190° C. to 296° C.
However, the aforementioned coatings comprising (polymeric) silicone resins have the disadvantage that high temperatures (190 to 296° C.) are necessary for complete curing. Furthermore, many silicone resin coatings in fact exhibit anti-adhesion properties, and inevitably exhibit poor bonding to the substrate. According to U.S. Pat. No. 4,4977,054, di- and trialkoxy-functional organosilanes, for example, therefore have to be added to these silicone resins in order to improve their adhesion.
The object of the present invention was therefore to provide coated particles, particularly particles having a content of inorganic materials, and particularly carrier particles for electrostatographic processes, wherein the particles have a magnetic core and a coating on the core which
a) is non-sticky, so that free-flowing particles which are predominantly free from agglomerates are obtained,
b) does not soften, even at elevated temperature,
c) prevents permanent adhesion and adhesive bonding of colour-imparting toners,
d) has a high resistance to abrasion,
e) adheres well to the particles, and
f) in the case of carrier particles for electrophotography has a good charging capacity, so that sufficient toner is taken up and can be released again.
The object of the present invention was also to provide a process for coating particles, particularly particles having a content of inorganic material, and particularly magnetic particles, which does not have the aforementioned disadvantages and which is characterised, for example, in that the deposition of the coating is effected in apparatuses which are as simple as possible by a simple process, and curing of the coating is effected at low temperatures.
Surprisingly, it has now been found that coated particles which do not have the aforementioned disadvantages are obtained, particularly coated particles containing inorganic material, if the coating is produced from monomeric polyfunctional organo-silanes and/or hydrolysis products thereof and/or reaction products thereof with organo-silanes containing hetero atoms and/or alkoxides.
The present invention therefore relates to particles (A) which are coated with a material (B), wherein particles (A) preferably contain inorganic material and are most preferably magnetic carrier particles for electrostatographic processes, and wherein material (B) is a monomeric, polyfunctional organosilane and/or a hydrolysis product thereof and/or a reaction product thereof with an organosilane containing a hetero atom and/or an alkoxide.
Organosilanes which contain hetero atoms in the sense of this invention consist of at least one silicon atom with hydrolysable and/or condensation crosslinking groups such as —SiOR, wherein R represents alkyl, cycloalkyl or aryl in particular, preferably alkyl, or consist of SiOH and at least one organic radical which contains a hetero atom and which is bonded via a carbon atom, which may be an alkyl, cycloalkyl or aryl radical. The hetero atoms of the organosilanes which contain hetero atoms are preferably N, P, S, F, Cl
Bellinghausen Rainer
Eickmans Johannes
Mager Michael
Tavernier Serge
Voets Raf
Agfa - Gevaert AG
Connolly Bove & Lodge & Hutz LLP
Le Hoa T.
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