Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-10-25
2002-06-04
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108300, C430S108400, C430S108600, C430S108700, C430S111410
Reexamination Certificate
active
06399264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developer for developing electrostatic latent images in electrophotography, electrostatic recording and electrostatic printing. More specifically, the present invention is directed to a composition and method that provides a developer which comprises at least positively charged particles, negatively charged particles and a lubricant to ensure the elimination of ghosting and system contamination, as well as maintaining a stable, high quality image, during extended use.
2. Description of the Background
Visible image forming methods associated with toners using electro-photographic systems have been extensively studied and are currently widely used. Typical examples of these techniques are dual-component developing methods, which use image-forming particles and often larger carrier particles, and mono-component developing methods, which use a toner comprising only magnetic or non-magnetic image-forming particles. Details of such developing methods are described in Kirk-Othmer,
Encyclopedia of Chemical Technology
, 4
th
ed., 9:261-275 (1994).
An image forming apparatus utilizing an electrophotographic method with toner is well known. In the image forming apparatus utilizing the electrophotographic method, images are generally formed onto a sheet of copy paper through the following processes.
After uniformly charging a photoconductor that serves as an image-holding body, images are exposed onto the surface of the charged photoconductor. Attenuating electrostatic charges during the exposure of light forms a latent image. Then the electrostatic latent images are visualized by developing with toner to form a toner image. The toner images are transferred onto the aforementioned medium and thereafter fixed on it by heating, pressure or solvent vapor.
In recent years, accompanying the rapid growth of computer technology, digital copiers and printers have been developed and become widely used. In these machines, monocomponent-developing methods have been applied more often to reduce the number of supply parts and ease of customer maintenance requirements compared with that of the dual component method.
In the mono-component systems, toner is generally required to have good fluidity and uniform chargeability in order to form a good quality visible image as described in U.S Pat. No. 5,802,284 incorporated herewithin by reference. The use of silica powder additives for toner particles to impart fluidity and chargeability properties has been widely studied and is one conventionally accepted method. Many US patents are known that include the use of silica or silicon dioxide with toner of various compositions. A subset of this prior art relates to surface treatments of silica or silicon dioxide for specific purposes to somehow enhance image quality characteristics relating to electrophotography. Examples of the use of hydrophobic silica particles for toner includes JP 46-5782 A, JP 48-47345A, and JP 48-47346A.
U.S. Pat. No. 5,464,722 and U.S. Pat. No. 5,447,815 disclose the manufacture of toners and the use of silicone oils and varnishes for treating toner additives, such as hydrophobic silica fine powder.
U.S. Pat. No. 4,868,084 includes the use of a silica treated with a silicone oil and alkyl silane or disilazane compound.
U.S. Pat. No. 5,702,858 and U.S. Pat. No. 5,561,019 are specific to the use of negatively charged hydrophobic silica treated with a silicone oil.
U.S. Pat. No. 4,902,570 discloses a process for treating metal oxides surfaces, such as silicon dioxide, by use of a modified ammonium-functional organopolysiloxane as a charge control substances for toners.
U.S. Pat. No. 4,618,556 discloses the use of a positive charge controller comprising fumed silica particles treated with a coupling agent bonded to either Si or Ti for use in a developer comprising a binder resin, colorant, and said positive charge controller.
U.S. Pat. No. 5,695,902 specifically describes the use of toner with an inorganic fine powder treated at least with silicone oil and a particular size composite metal oxide containing Si and Sr.
U.S. Pat. No. 6,004,711 discloses a toner composition with an extra-particulate additive having a negative charge and a second extra-particulate additive having a positive charge. This patent is concerned with addressing a problem of a wavy patterns formed when using a recoated or worn developer magnetic roller. The patent discloses that the toner composition therein includes conventional toner components in conventional amounts including zinc stearate, abrasives, microspheres, and the like.
Electrophotographic systems have also been known to include metal salts of fatty acids. For example, JP09-236942 discloses such metal salts to avoid the toner filming of an organic photoconductor (OPC) with the aid of cleaning blades. The metallic salt works to reduce this filming of the OPC drum and together with the use of spherical toner, filming has been shown to be greatly reduced. As the concentration of metallic fatty acid salts increase, the toner accepts charge more readily within a specified range. In this work, it was also found that if Ds50/Dt50>0.6, wherein Ds50 represents the volume median particle size of metallic salts of fatty acids and Dt50 represents the volume median particle size of the toner component particles, contamination of the laser printer machine components will occur resulting in prints with high background. If Ds84/Ds16>6, wherein Ds 84 represents the diameter at 84% of the accumulated undersize distribution curve of the metallic fatty acid particles and Ds16 represents the diameter at 16% of the accumulated undersize distribution curve of the metallic fatty acid particles, then the uniformity of the metallic salts of fatty acids particle size is broad and the charging stability exhibited in the toner is not acceptable. These particle size and particle size distribution values are as determined by a dry measurement technique using a Heros and Redos laser diffraction instrument manufactured by Sympatec.
In the actual toner composition product design, the silica particles must be carefully selected to minimize side effects such as environmental instability, ghosting, photo-conductor contamination, and photo-conductor charging system contamination as well as any adverse side-effects on image quality. Generally, silica particles have a finer particle size than toner particles and therefore the silica particles possess a larger specific surface area and higher charging properties which can largely influence overall toner performance.
Environmental stability improvement by modification of the silica surface with chemical treatment has been widely studied and reported. Hydrophobic treatment is an established method of providing environmental stability to the toner.
Ghosting is a typical defect often seen in monocomponent development systems and can be described as developed image forming toner patterns on a latent image-retaining member, which are electrostatically transferred to a transfer material such as paper and form either lighter images than the background or darker images than the background. In instances where the ghost image is lighter than the background, this phenomena is known as “negative ghosting” and where the ghost image is darker than the background, this phenomenon is known as “positive ghosting.” Because the ghosting phenomenon is complex and results from actual electrostatic printer orcopy machine system characteristics, toner flowability, toner triboelectric charge properties, and even exponential memory decay time of the photoconductor, the root cause is still not perfectly understood. It is often possible; however, to measure the distance between ghost images to determine which component makes the larger contribution to this undesirable imaging characteristic.
If the ghost image (negative or positive type) appears on the transfer material (paper) in proportion to the photoconductor circumference, this can usually be attributed to the photoconducti
Hirama Kazuhiro
Ogata Kenzo
Saiki Shinichi
Dote Janis L.
Mitsubishi Chemical America, Inc.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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