Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-08-23
2002-03-19
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111330, C430S137210
Reexamination Certificate
active
06358656
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to toners, and particularly toner treatment compositions.
BACKGROUND OF THE INVENTION
Toners can be used for various applications, including electrographics. Such applications can require toners for printing high quality text and half tone images (see S. Sata et al., “Study on the Surface Properties of Polyester Color Toner,”
IS
&
T NIP
13, 149-152 (1997) and Nash, R. & Muller, R. N. “The Effect of Toner and Carrier Composition on the Relationship Between Toner Charge to Mass Ratio and Toner Concentration,”
IS
&
T NIP
13, 112-120 (1997).
In electrographic applications, it is generally desirable to reduce toner particle size in a developer to improve image quality. However, the smaller the toner particles, the more likely that the particles will pack in an electrographic apparatus, such as a copier, and not flow properly, thus adversely affecting the apparatus's operation and image quality.
One solution can be adding fumed silica as a lubricant to reduce friction and packing, and thus improve the fluidity of the pre-toner particles. However, the use of fumed silica can result in an increase in the negative charge of the treated toner particles. Such a negative charge increase can impede transport of a particle, particularly in multilayer transfer processes in color printers, from one charged surface to another during electrographic operations, e.g., from the developer station to the photoconductor, or from the photoconductor onto the paper.
Alternatively, toner particles can be treated with titanium dioxide. Such formulations are disclosed in U.S. Pat. Nos. 4,943,506, 5,155,000, 5,192,637, 5,429,902, 5,705,303 and 5,747,211. Titanium dioxide treated toners generally have lower charges, and thus are easier to transport through the electrographic apparatus. However, such titanium dioxide treated toners, partly due to their low charge, can create significant airborne dust when replenishing an aged developer, which can include a carrier and a toner, with fresh toner. Such replenishment methods are disclosed in U.S. Pat. Nos. 3,938,992 and 3,944,493.
Attempts have been made to treat toner particles with a combination of silica and titanium dioxide mixtures, as disclosed in U.S. Pat. Nos. 5,272,040, 5,776,646 and 4,623,605, but these efforts have been largely unsuccessful in simultaneously reducing negative toner particle charge and rebuilt airborne dust levels.
SUMMARY OF THE INVENTION
The present invention provides a treatment for an electrographic toner. Generally, the treatment includes at least one titanium dioxide particle having a BET surface area of at least about 70 m
2
/g and/or a diameter no more than about 20 nm, and at least one silica particle. Preferably, the titanium dioxide particle has a BET surface area of at least about 80 m
2
/g, and more preferably a BET surface area of from about 75 to about 105 m
2
/g. In addition, the titanium dioxide particle generally has a diameter of no more than about 15 nm, and preferably still, has a diameter of about 7 to about 12 nm. Preferably, the weight ratio of silica particles to titanium particles can be from about 1:0.1 to about 1:2, and more preferably, the weight ratio of silica particles to titanium particles can be from about 1:0.5 to about 1:1.5, and optimally, about 1:1.
The present invention additionally provides an electrographic toner, including at least one toner particle. This particle can include a binder, a pigment and a charge control agent. The toner particle can be treated with the titanium dioxide-silica treatment as discussed above. Preferably, the treatment is applied to the surface of the particle. What is more, the electrographic toner can have a BET surface area to Coulter surface area of 1:1 to 3:1, and 8 micron average particle size. The invention is further directed to a developer including the electrographic toner as discussed above and a carrier. The developer preferably exhibits a charged mass of 10-40 (microCoulomb)/gram, and a rebuilt charge at 10 minutes of less than −45 (microCoulomb)/gram and less than 5 milligrams of generated airborne dust after rebuilding.
Additionally, the present invention provides a method of making a toner. The method includes providing at least one toner particle and treating with at least one titanium dioxide particle having a BET surface area of at least about 70 m
2
/g and at least one silica particle.
Definitions
“Airborne dust” refers to dust that is produced when fresh replenishment toner is mixed with aged developer.
As used herein, the term “electrographic” is generally interchangeable with the terms “electrostatographic”, “electrophotographic”, and “xerographic”.
“Charge characteristics” refers to the ratio of charge to mass of a toner in a developer. Preferably, an 8 micron (volume average) particularized toner has a charged mass ratio of 10-50 microCoulomb/gram, and more preferably, 20-45 microCoulomb/gram.
The “Coulter counter” measures the number in volume of average particle sizes and the specific surface area of a toner. This measurement is made by suspending the particles in a conductive liquid and monitoring the electrical current between two electrodes emerged in the conductive liquid on either side of a small aperture. The suspension of particles flows through the aperture. Each particle changes the impedance between the electrodes and produces an electric pulse of short duration having a magnitude essentially proportional to the particle volume. The series of pulses are electrically scaled, counted and accumulated in a number of size-related channels, thereby producing a size distribution curve. Assuming the particles are spherical, the Coulter counter also estimates a specific surface area of the toner particles.
The “BET” is a measurement of a particles surface area in square meters per gram. This procedure includes degassing a sample overnight under helium gas at 10 psi pressure at room temperature and then subjecting the degassed sample to a flowing mixture of about 70 mol % helium carrier gas and about 30 mol % nitrogen absorbate gas at a pressure of 7 psi and −195 degrees C. The amount of nitrogen adsorbed is used with the BET equation to calculate the surface area. What is more, the ratio of the BET surface area to the Coulter surface area can be used as a measure of the toner shape irregularity.
As used herein, the term “rebuilt charge” refers to the charge associated with the fresh replenishment toner particles after introducing and mixing with carrier from an aged developer.
Discussion
One embodiment of the invention is a treatment composition for an electrographic toner. The treatment can include at least one titanium dioxide particle having a BET surface area of at least about 70 m
2
/g and preferably having a BET surface area of from about 75 to about 105 m
2
/g. What is more, preferably the treatment has at least one titanium dioxide particle having a BET of at least about 80 m
2
/g. Generally, multiple titanium dioxide particles are used. Furthermore, the titanium dioxide particles used in the present invention preferably have a diameter of not more than about 20 nm, preferably not more than about 15 nm, and more preferably have a diameter ranging from about 7 to about 12 nm. An example of such titanium dioxide particles are those sold under the trade designation MPT313 by Isihara Sangyo Kaisha Ltd of Osaka, Japan.
The treatment can further include a silica particle. Generally, multiple silica particles are used. Preferably, such silica particles have a BET surface area of from about 50- about 350 m
2
/g and an average particle diameter of about 5-about 40 nm, and more preferably an average particle diameter of about 8-about 20 nm. Examples of such silica particles are those sold under the trade designations R972, RY200 and RY300 from Degussa Corporation, of Akron, Ohio.
Optionally, the silica and/or titanium dioxide particles may be treated with one or more organic or silicone compounds in an amount, preferably, of between about 0.1 to about 20 weight percent
Goebel William Keith
Srinivasan Satyanarayan
Tyagi Dinesh
Goodrow John
Kessler Lawrence P.
NexPress Solutions LLC
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