Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-07-10
2003-01-07
Chapman, Mark A. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S137100
Reexamination Certificate
active
06503677
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to emulsion aggregation toners coated with a coating comprised of a mixture of a negatively chargeable additive and a positively chargeable additive, a method of making such coated emulsion aggregation toners, and a method of preparing a developer that contains such coated toner particles and exhibits rapid admix and little or no charge through.
2. Discussion of Related Art
Hybrid scavengeless development (HSD) technology develops toner via a conventional magnetic brush onto the surface of a donor roll. A plurality of electrode wires is closely spaced from the toned donor roll in the development zone. An AC voltage is applied to the wires to generate a toner cloud in the development zone. This donor roll generally consists of a conductive core covered with a thin, for example 50-200 m, partially conductive layer. The magnetic brush roll is held at an electrical potential difference relative to the donor core to produce the field necessary for toner development. The toner layer on the donor roll is then disturbed by electric fields from a wire or set of wires to produce and sustain an agitated cloud of toner particles. Typical AC voltages of the wires relative to the donor are 700-900 Vpp at frequencies of 5-15 kHz. These AC signals are often square waves, rather than pure sinusoidal waves. Toner from the cloud is then developed onto the nearby photoreceptor by fields created by a latent image. To operate effectively within these operating parameters, imaging devices employing HSD require toners that charge at high levels, for example between about −30 &mgr;C/g and about −45 &mgr;C/g.
The properties of a toner are set through the selection of materials and amounts of the materials of the toner. The charging characteristics of a toner are also dependent upon the carrier used in a developer composition, in particular the carrier coating. Toners typically comprise at least a binder resin, a colorant and one or more external surface additives. The external surface additives are generally added in small amounts. Examples of external surface additives include, for example, silica, titanium dioxide, zinc stearate, etc.
Toners having a triboelectric charging property within the range of about −30 &mgr;C/g and about −45 &mgr;C/g may be achieved when using small sized silica particles as external additives, for example silica particles having average sizes less than 20 nm, such as, for example, R805 (~12 nm) and/or R972 (~16 nm). However, the developability at areas of low toner area coverage degrade over time. This has been attributed to the small sized additives being impacted into the toner surface over time.
The above problem with small sized additives has been addressed by using larger sized additives, i.e., additives having a size of 40 nm or larger such as, for example, RX50 silica, RX515H silica or SMT5103 titania. However, although the above problem is addressed, the toners do not exhibit as high a triboelectric charging ability and also exhibit charge through (discussed more fully below). Moreover, new carrier coatings are being developed that enable higher charging developers, particularly those with larger size additive packages, but when such developers are tested at low area coverage followed by high area coverage, the developers tend to exhibit low or wrong sign toner due to charge through, i.e., the incumbent toner in the device becomes less negative or even wrong sign, i.e., positive, and the new (fresh) toner added may charge very negative. The presence of low charge and/or wrong sign toner can result in objectionable background.
U.S. Pat. No. 6,087,059, incorporated herein by reference in its entirety, describes a toner comprised of resin, colorant and a surface additive mixture comprised of two coated silica's, and a coated metal oxide, and wherein the two coated silica's are comprised of a first silica and a second silica, and wherein the first coated silica contains a coating of an alkyl silane and an amino alkyl silane.
U.S. Pat. No. 6,210,851, incorporated herein by reference in its entirety, describes an electrostatographic toner comprising toner particles that have been surface treated with a solvent and silica particles having a BET surface area of 40 to 400 m
2
/g; wherein the solvent is selected from aliphatic alcohols, diols and triols, aliphatic ketones, aliphatic esters, cyclic ethers and aliphatic ethers.
U.S. Pat. No. 5,484,675, incorporated herein by reference in its entirety, describes a toner composition comprised of resin and pigment particles where the pigment particles are treated with a fluorosilane polymer.
U.S. Pat. No. 4,973,540 describes a developer for developing electrostatic latent images formed on an electrostatic latent image carrier, which comprises a toner including; a resin, a colorant, and an inorganic fine particle with at least both a negatively chargeable polar group and a positively chargeable polar group on the surface of the inorganic fine particle. The negatively chargeable polar group contains fluorine atoms at a content of from 0.005 to 6% and the positively chargeable polar group contains nitrogen atoms at a constant of from 0.04 to 5%, the contents being selected within these ranges to provide the inorganic fine particle with either.a positive or negative charge. The inorganic fine particles are selected from the group consisting of silicon dioxide, silicate, titanium dioxide, alumina, magnesium carbonate, barium titanate and zinc oxide.
U.S. Pat. No. 5,429,873 describes surface-modified, pyrogenically produced silicon dioxide obtained by placing a pyrogenically produced silicon dioxide in a mixing device, spraying it with a chemical compound from the group: CHF
2
—CF
2
—O—(CH
2
)
3
—Si(OCH
3
)
3
, CF
3
—CHF—CF
2
—O—(CH
2
)
3
—Si(OCH
3
)
3
, C
4
F
9
—CH
2
—Si
2
—(OCH
3
)
3
, and C
6
F
13
—CH
2
—CH
2
—Si(OCH
3
)
3
with intensive mixing, subsequently mixing it and tempering the mixture obtained for a fairly long time. The surface-modified silicon dioxide is described to be used in toners.
U.S. Pat. No. 5,376,172, incorporated herein by reference in its entirety, describes a process for preparing silane modified metal oxides comprising reacting a metal oxide with an amine compound with or without water present on the surface of the metal oxide to form an amine metal oxide surface intermediate, optionally removing excess unreacted amine, and subsequently reacting the intermediate with an organosilane. The organosilane is of the formula Si(X)
n
(R
m
)
4−n
where Si is a silicon atom, X is a leaving group selected from the group consisting of halogen and alkoxy, R is an alkyl, alkenyl, alkynyl, aryl, alkaryl, aralkyl, or the halogenated derivatives thereof; m is an integer with a value of at least 1; and n is an integer of 1 to 3.
What is still desired is a toner having a surface additive package that substantially eliminates charge through and slow admix, as well as enables high triboelectric charging, and which toner is particularly suitable for use in an imaging device utilizing HSD.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to develop a toner capable of high triboelectric charging but that does not exhibit charge through or slow admix.
It is a still further object of the present invention to develop a surface additive package for a toner that enables the foregoing properties.
It is a still further object of the present invention to develop a toner and developer that can be suitably used in an imaging device employing hybrid scavengeless development.
These and other objects of the present invention are achieved herein, wherein in embodiments the invention relates to an emulsion aggregation toner comprised of toner particles comprising polymer binder and colorant and a surface additive package comprising at least one additive negatively chargeable to a reference carrier (negative additive) and at least one additive positively chargeable to a reference carrier (positive
Grushkin Bernard
Gutman Edward J.
Ruhland John G.
Chapman Mark A.
Oliff & Berridg,e PLC
Palazzo Eugene O.
Xerox Corporation
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